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Over the last 150 years, large stretches of salmon habitat have been e

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Over the last 150 years, large stretches of salmon habitat have been e  [#permalink]

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New post Updated on: 30 Jul 2019, 04:17
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Over the last 150 years, large stretches of salmon habitat have been eliminated by human activity: mining, livestock grazing, timber harvesting, and agriculture as well as recreational and urban development. The numerical effect is obvious: there are fewer salmon in degraded regions than in pristine ones; however, habitat loss also has the potential to reduce genetic diversity. This is most evident in cases where it results in the extinction of entire salmon populations. Indeed, most analysts believe that some kind of environmental degradation underlies the demise of many extinct salmon populations. Although some rivers have been recolonized, the unique genes of the original populations have been lost.

Large-scale disturbances in one locale also have the potential to alter the genetic structure of populations in neighboring areas, even if those areas have pristine habitats. Why? Although the homing instinct of salmon to their natal stream is strong, a fraction of the fish returning from the sea (rarely more than 15 percent) stray and spawn in nearby streams. Low levels of straying are crucial, since the process provides a source of novel genes and a mechanism by which a location can be repopulated should the fish there disappear. Yet high rates of straying can be problematic because misdirected fish may interbreed with the existing stock to such a degree that any local adaptations that are present become diluted. Straying rates remain relatively low when environmental conditions are stable, but can increase dramatically when streams suffer severe disturbance. The 1980 volcanic eruption of Mount Saint Helens, for example, sent mud and debris into several tributaries of the Columbia River. For the next couple of years, steelhead trout (a species included among the salmonids) returning from the sea to spawn were forced to find alternative streams. As a consequence, their rates of straying, initially 16 percent, rose to more than 40 percent overall.

Although no one has quantified changes in the rate of straying as a result of the disturbances caused by humans, there is no reason to suspect that the effect would be qualitatively different than what was seen in the aftermath of the Mount Saint Helens eruption. Such a dramatic increase in straying from damaged areas to more pristine streams results in substantial gene flow, which can in turn lower the overall fitness of subsequent generations.
VRC000460-01
1. The primary purpose of the passage is to

(A) argue against a conventional explanation for the extinction of certain salmon populations and suggest an alternative
(B) correct a common misunderstanding about the behavior of salmon in response to environmental degradation caused by human activity
(C) compare the effects of human activity on salmon populations with the effects of natural disturbances on salmon populations
(D) differentiate the particular effects of various human activities on salmon habitats
(E) describe how environmental degradation can cause changes in salmon populations that extend beyond a numerical reduction




VRC000460-02
2. It can be inferred from the passage that the occasional failure of some salmon to return to their natal streams in order to spawn provides a mechanism by which

(A) pristine streams that are near polluted streams become polluted themselves
(B) the particular adaptations of a polluted stream’s salmon population can be preserved without dilution
(C) the number of salmon in pristine habitats decreases relative to the number in polluted streams
(D) an environmentally degraded stream could be recolonized by new salmon populations should the stream recover
(E) the extinction of the salmon populations that spawn in polluted streams is accelerated




VRC000460-03
3. According to the passage, human activity has had which of the following effects on salmon populations?

(A) An increase in the size of salmon populations in some previously polluted rivers
(B) A decline in the number of salmon in some rivers
(C) A decrease in the number straying salmon in some rivers
(D) A decrease in the gene flow between salmon populations that spawn in polluted streams and populations that spawn in pristine streams
(E) A decline in the vulnerability of some salmon populations to the effects of naturally occurring habitat destruction




4. [Not An official Question]The author mentions the “aftermath of the Mount Saint Helens eruption” most likely in order to

(A) provide an example of the process that allows the repopulation of rivers whose indigenous salmon population has become extinct
(B) indicate the extent to which the disturbance of salmon habitat by human activity in one stream might affect the genetic structure of salmon populations elsewhere
(C) provide a standard of comparison against which the impact of human activity on the gene flow among salmon populations should be measured
(D) show how salmons’ homing instinct can be impaired as a result of severe environmental degradation of their natal streams
(E) show why straying rates in salmon populations remain generally low except when spawning streams suffer severe environmental disturbance


C - Not an official Question


VRC000460-05
5. The author's argument that increased straying can "lower the overall fitness of subsequent generations" (see hightlited text) is based on which of the following assumptions?

(A) A disturbance of salmonid spawning streams caused by human activity could increase the straying rate of affected salmonid populations as much as the aftermath of the Mount Saint Helens eruption did.
(B) In the streams in which the straying salmonids spawn, these straying salmonids would amount to no more than 40 percent of the total spawning population
(C) Salmonids in some streams benefit from particular local adaptions.
(D) Nonenvironmental factors have no effect on salmonid straying rates.
(E) At least some of the streams in which straying salmonids would spawn are pristine, affected by neither natural nor artificial disturbances.




VRC000460-07
6. Which of the following does the author mention as support for the view that environmental disturbances caused by human activity could increase straying rates?

(A) The existence of salmon populations in rivers where the elimination of salmon habitat by human activity had previously made the fish extinct
(B) The results of studies measuring the impact on straying rates of habitat loss caused by human activity
(C) The potential for disturbances in one environment to cause the introduction of novel genes into salmon populations in neighboring areas
(D) The weaknesses in the view that the extinction of entire salmon populations is the only mechanism by which human destruction of salmon habitat reduces genetic diversity in salmon
(E) The absence of any reason for believing that disturbances brought about by human activitiy would differ in their effects from comparable disturbances brought about by natural causes




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Last edited by SajjadAhmad on 30 Jul 2019, 04:17, edited 6 times in total.
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Re: Over the last 150 years, large stretches of salmon habitat have been e  [#permalink]

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New post 26 Jul 2012, 06:38
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1
Q10:
It can be inferred from the passage that the occasional failure of some salmon to return to their natal streams in order to spawn provides a mechanism by which

a. pristine streams that are near polluted streams become polluted themselves
b. the particular adaptations of a polluted stream’s salmon population can be preserved without dilution
c. the number of salmon in pristine habitats decreases relative to the number in polluted streams
d. an environmentally degraded stream could be recolonized by new salmon populations should the stream recover
e. the extinction of the salmon populations that spawn in polluted streams is accelerated

As given in line 20 “Although some rivers have been recolonized, the unique genes of the original populations have been lost.” This refers that some streams have been initially “DE SALMONed” i.e Salmons fail to return to their natal streams in order to spawn because of some environmental degradation of the stream but somehow the stream was restored and finally recolonized. That’s exactly what option D says (If the stream recovers, an environmentally degraded stream could be recolonized).

Q11:
According to the passage, human activity has had which of the following effects on salmon populations?

a. An increase in the size of salmon populations in some previously polluted rivers
b. A decline in the number of salmon in some rivers
c. A decrease in the number straying salmon in some rivers
d. A decrease in the gene flow between salmon populations that spawn in polluted streams and populations that spawn in pristine streams
e. A decline in the vulnerability of some salmon populations to the effects of naturally occurring habitat destruction


As given in opening lines “Over the last 150 years, large stretches of salmon habitat have been eliminated by human activity: Line mining, livestock grazing, timber harvesting, and agriculture as well as recreational and urban development. The numerical effect is obvious: there are fewer salmon in degraded regions than in pristine ones;” This clearly refers that human activity caused decline in number of salmons in some river (B)

Q12:
The author mentions the “aftermath of the Mount Saint Helens eruption” (lines 73-74) most likely in order to

a. provide an example of the process that allows the repopulation of rivers whose indigenous salmon population has become extinct
b. indicate the extent to which the disturbance of salmon habitat by human activity in one stream might affect the genetic structure of salmon populations elsewhere
c. provide a standard of comparison against which the impact of human activity on the gene flow among salmon populations should be measured
d. show how salmons’ homing instinct can be impaired as a result of severe environmental degradation of their natal streams
e. show why straying rates in salmon populations remain generally low except when spawning streams suffer severe environmental disturbance

As given in last para “Although no one has quantified changes in the rate of straying as a result of the disturbances caused by humans, there is no reason to suspect that the effect would be qualitatively different than what was seen in the aftermath of the Mount Saint Helens eruption”, author is clearly comparing the effect of human activity with that of environmental degradation.

a. provide an example of the process that allows the repopulation of rivers whose indigenous salmon population has become extinct – Not an example of any process of repopulation
b. indicate the extent to which the disturbance of salmon habitat by human activity in one stream might affect the genetic structure of salmon populations elsewhere – not talking about any particular stream
c. provide a standard of comparison against which the impact of human activity on the gene flow among salmon populations should be measured - YES
d. show how salmons’ homing instinct can be impaired as a result of severe environmental degradation of their natal streams – Clearly out
e. show why straying rates in salmon populations remain generally low except when spawning streams suffer severe environmental disturbance – Clearly out
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Re: Over the last 150 years, large stretches of salmon habitat have been e  [#permalink]

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New post 17 Oct 2012, 07:22
Hey in the first question, we are asked to provide an "inference" which MUST be true according to the passage!
Also, the passage says nothing about dilution during low levels of straying. It just says that with low levels of straying, there is a solid mix of new genes which could be good for the area. That is the are could or could not benefit from low straying. It becomes crucial if the population of fishes decline in the other area which could be increased by moderate level of straying. (please note that the new population could or could not be diluted: not indicated in the passage). It just means that low levels of straying could save a dying fish population.
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Re: Over the last 150 years, large stretches of salmon habitat have been e  [#permalink]

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New post 17 Oct 2012, 10:17
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voodoochild wrote:
It can be inferred from the passage that the occasional failure of some salmon to return to their natal streams in order to spawn provides a mechanism by which
a. pristine streams that are near polluted streams become polluted themselves
b. the particular adaptations of a polluted stream’s salmon population can be preserved without dilution
c. the number of salmon in pristine habitats decreases relative to the number in polluted streams
d. an environmentally degraded stream could be recolonized by new salmon populations should the stream recover
e. the extinction of the salmon populations that spawn in polluted streams is accelerated


OA D

Why is B wrong? When high straying happens, dilution is the issue. Hence, when low straying happens, dilution is not an issue at all -- what B) says. Also lines (30), " Low levels of straying are crucial, since the process provides a source of novel genes and a mechanism by which a location can be (40) repopulated should the fish there disappear. " --- implies genes are preserved -- and as the next sentence says "dilution happens" in case of high straying. Can't we infer that in case of low straying, no dilution happens and the genes are preserved?

B is quite wrong because the passage makes very clear --- when a stream is polluted, straying happens, which means dilution happens. The passage describes clearly the straying that resulted from the Mount St. Helen's eruption, and then around line (70) says that the effect of pollution probably would be about the same as what they saw at Mount St. Helen's. When the stream is polluted, the salmon can't use it to spawn, so they stray.

voodoochild wrote:
The author's argument that increased straying can "lower the overall fitness of subsequent generation" (see highlighted text) is based on which of the following assumptions?
a) a disturbance of salmonid spawning streams caused by human activtity will increasing the straying rate of affected salmonid populations as much as the aftermath of the Mount Saint Helens eruption did.
b) In the streams in which the straying salmonids spawn, these straying salmonids would amount to no more than 40 percent of total spawning population
c) Salmonids in some streams benefit from particular local adaptations
d) Nonenvironmental factors have no effect
e) At least some of the streams in which straying salmonids would spawn are pristine, affected by neither natural nor artificial disturbances.


OA C


Why is E) wrong? Also what support do we have for C) To me, "lowering the overall fitness" implies less likely to pass Darwin's "survival of the fittest" Hence, such adaptations are in fact bad -- 180 to what the OA is :( To me, the conclusion is that straying because of human effects causes bad things to Salmon in pristine streams. What's the support? Straying causing the dilution of the gene pool. I couldn't find that answer choice.

You're correct in your understanding of "fitness" --- we are talking about Darwinian fitness here.

The passage says "high rates of straying can be problematic because misdirected fish may interbreed with the existing stock to such a degree that any local adaptations that are present become diluted." In other words, the salmon in those pristine areas had adaptions particular suited to those areas, which made them quite fit, and along come a bunch of salmon from the polluted stream next door, and they genetically dilute the salmon of that pristine stream, making them less adapted to that unique niche, and hence less fit. That passage is enormous support for (C)

(E) is a typically GMAT RC distractor, and you fell for the bait. It is a statement that's true in general, but not relevant to the argument. Suppose we said that there was no such thing as a "pristine" perfect place for salmon --- suppose even the environments with zero pollution had natural challenges. Well, then, the salmon in those environments, over the centuries, would adapt to those particular conditions and be quite fit, and then if others stray into their unique stream and interbreed with them, it will reduce the fitness of that population.

Does all this make sense?

Mike :-)
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Re: Over the last 150 years, large stretches of salmon habitat have been e  [#permalink]

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New post 18 Oct 2012, 22:21
Mike,
Thanks for your kind reply. I am not clear, and I am still confused about both the answer choices.

mikemcgarry wrote:
B is quite wrong because the passage makes very clear --- when a stream is polluted, straying happens, which means dilution happens. The passage describes clearly the straying that resulted from the Mount St. Helen's eruption, and then around line (70) says that the effect of pollution probably would be about the same as what they saw at Mount St. Helen's. When the stream is polluted, the salmon can't use it to spawn, so they stray.



For the first one, as you have stated above, I think that both of us are on the same page : when the stream gets polluted, the polluted stream's salmon population cannot spawn, and hence they have to find other stream to spawn, leading to straying. Isn't this same as saying "preserving without dilution" i.e. the polluted stream's population can be preserved when there is low-level of straying? Now to extend this idea - why do I think that we can preserve the polluted stream's population? It's because in lines 35-40 it's stated that their genes can be preserved. I am still not able to see why B) is incorrect.

I see dear Douvik's point in that "dilution" is not explicitly stated while discussing 'low levels of straying.' I am not sure whether these are grounds to eliminate B. The passage does talk about high-levels of straying, and has explicitly stated that low-levels of straying is better than high-level straying because of the dilution issue. Can't we infer that the dilution doesn't happen in the case of low-level straying. I am not sure about this. It seems logical to me and within the boundaries of the passage.


mikemcgarry wrote:

(E) is a typically GMAT RC distractor, and you fell for the bait. It is a statement that's true in general, but not relevant to the argument. Suppose we said that there was no such thing as a "pristine" perfect place for salmon --- suppose even the environments with zero pollution had natural challenges. Well, then, the salmon in those environments, over the centuries, would adapt to those particular conditions and be quite fit, and then if others stray into their unique stream and interbreed with them, it will reduce the fitness of that population.


For the second one, this is a great 'assumption' question. Let's dissect this further. Conclusion: "Disturbances cause by humans lower the overall fitness of subsequent generation in 'mixed' streams." Premise, as you stated, the salmon in those pristine areas had adaptions particular suited to those areas, which made them quite fit, and along come a bunch of salmon from the polluted stream next door, and they genetically dilute the salmon of that pristine stream, making them less adapted to that unique niche, and hence less fit. I agree 100%. That was my understanding as well. However, I am still not able to see the correctness of C).

No let's negate C - Salmonids in none of the streams benefit from particular local adaptations. In my opinion, this has no effect on the conclusion. The conclusion is about comparing the overall fitness levels between "pristine" population (i.e. native population) and "mixed" population (i.e. native + newly strayed ones). Who cares whether 1% of population benefits from the adaptation or 90% of the native population benefits from the adaptation. We are concerned about the causal link between human activity and the lowering of the overall fitness. It could be possible that the native population is only 1% fit, and the straying would decrease this further down to 0.05%. Do I care about the level of fitness of the native population? No. I am only concerned about the "lowering" of fitness. I am still not clear.

Now let's negate E- (I must admit that while solving this question, I was unsatisfied with all the answer choices and had no option than to choose E) from C and E (50% chance :( ) ) -- I agree that we don't care whether the pristine streams are affected by natural disaster or not. We are only concerned about the link between "human activity" and the lowering of overall Darwinian fitness.



Can you please help me? I am really confused.


Thanks
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New post 21 Aug 2016, 15:24
tae808 wrote:
Is the word "stream" in this passage and questions refer to habitat?
stream=habitat?
Please comment!!

Dear tae808,

I'm happy to respond my friend. :-)

A "habitat" is the environment in which a living thing is designed to live, the place where it naturally thrives. For a deer, the habitat is a forest. For a giraffe, the habitat is the Serengeti. For a salmon, the habitat, for at least part of its life cycle, is a stream. Many things live in a healthy stream, so for these animals, it is a habitat. Does this make sense?

Mike
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Re: Over the last 150 years, large stretches of salmon habitat have been e  [#permalink]

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New post 03 Apr 2017, 06:48
3
RMD007 wrote:
Nightmare007 wrote:
Nightmare007 wrote:
6 min My answers are E D B E . Can you explain me the answer for 12th


I think 12th question answer should be C instead of E if we think about the lines in last paragraph .


6 Mins :o that's awesome!! To read the paragraph itself it took 6 mins for me :P Any tips sir..

I took 12 minutes, all correct.. Yes, last one should be C.



- Read question first - Ignore all the relative clauses , dependent clauses and Examples ; Make structure words exception . Map the paragraph in maximum 4 - 5 words .
General question - guess first
Detail question - use map to come to parah and check
Well i guess this is what a GMAT preparing guy should do. Rather than understanding whole parah and answering form memory.
Think RC is BIG CR question, where background info plays no role.
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New post 19 Jun 2017, 05:32
mikemcgarry wrote:
tae808 wrote:
Is the word "stream" in this passage and questions refer to habitat?
stream=habitat?
Please comment!!

Dear tae808,

I'm happy to respond my friend. :-)

A "habitat" is the environment in which a living thing is designed to live, the place where it naturally thrives. For a deer, the habitat is a forest. For a giraffe, the habitat is the Serengeti. For a salmon, the habitat, for at least part of its life cycle, is a stream. Many things live in a healthy stream, so for these animals, it is a habitat. Does this make sense?

Mike


Dear Mike,
Hope you can help with this question

6. Which of the following does the author mention as support for the view that environmental disturbances caused by human activity could increase straying rates?

(A) The existence of salmon populations in rivers where the elimination of salmon habitat by human activity had previously made the fish extinct
(B) The results of studies measuring the impact on straying rates of habitat loss caused by human activity
(C) The potential for disturbances in one environment to cause the introduction of novel genes into salmon populations in neighboring areas
(D) The weaknesses in the view that the extinction of entire salmon populations is the only mechanism by which human destruction of salmon habitat reduces genetic diversity in salmon
(E) The absence of any reason for believing that disturbances brought about by human activitiy would differ in their effects from comparable disturbances brought about by natural causes

I cannot find any support for option D.
No where in the passage does it say or imply " elimination of entire salmon population is the only way that leads to reduction in genetic diversity"

So the question of weakness in this view does not arise.

I thought answer for this question should be E.

May be I am missing something. Thanks for your help.
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Re: Over the last 150 years, large stretches of salmon habitat have been e  [#permalink]

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New post 20 Jun 2017, 01:12
1
stne wrote:
mikemcgarry wrote:
tae808 wrote:
Is the word "stream" in this passage and questions refer to habitat?
stream=habitat?
Please comment!!

Dear tae808,

I'm happy to respond my friend. :-)

A "habitat" is the environment in which a living thing is designed to live, the place where it naturally thrives. For a deer, the habitat is a forest. For a giraffe, the habitat is the Serengeti. For a salmon, the habitat, for at least part of its life cycle, is a stream. Many things live in a healthy stream, so for these animals, it is a habitat. Does this make sense?

Mike


Dear Mike,
Hope you can help with this question

6. Which of the following does the author mention as support for the view that environmental disturbances caused by human activity could increase straying rates?

(A) The existence of salmon populations in rivers where the elimination of salmon habitat by human activity had previously made the fish extinct
(B) The results of studies measuring the impact on straying rates of habitat loss caused by human activity
(C) The potential for disturbances in one environment to cause the introduction of novel genes into salmon populations in neighboring areas
(D) The weaknesses in the view that the extinction of entire salmon populations is the only mechanism by which human destruction of salmon habitat reduces genetic diversity in salmon
(E) The absence of any reason for believing that disturbances brought about by human activitiy would differ in their effects from comparable disturbances brought about by natural causes

I cannot find any support for option D.
No where in the passage does it say or imply " elimination of entire salmon population is the only way that leads to reduction in genetic diversity"

So the question of weakness in this view does not arise.

I thought answer for this question should be E.

May be I am missing something. Thanks for your help.



I'm also having trouble with this one. This is probably wrong but this is the only way I can make the OA fit.

(D) The weaknesses in the view that the extinction of entire salmon populations is the only mechanism by which human destruction of salmon habitat reduces genetic diversity in salmon

what are the weaknesses mentioned?

There is only one as far as I can tell and that is by introducing another possible mechanism by which human destruction of Salmon habitat could reduce genetic diversity. Severe disturbances caused by natural disasters have led to an increase in straying which could limit genetic diversity if as indicated the fish that stray interbreed with the existing stock to such a degree that any local adaptations that are present become diluted. It then goes on to say that environmental disturbances caused by human destruction would likely have the same effect (the reason for the confusion with E.)

So what supports the idea that environmental disturbances caused by human activity could increase straying rates? (D) The fact that environmental disturbances caused by natural disasters have lead to an increase in straying.


(E) The absence of any reason for believing that disturbances brought about by human activity would differ in their effects from comparable disturbances brought about by natural causes

My thinking is that E. might need to be combined with D. for it to be in support and so not correct.

I really hope one of the experts could explain the logic behind this question.
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Re: Over the last 150 years, large stretches of salmon habitat have been e  [#permalink]

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New post 20 Jun 2017, 21:52
6. Which of the following does the author mention as support for the view that environmental disturbances caused by human activity could increase straying rates?

(A) The existence of salmon populations in rivers where the elimination of salmon habitat by human activity had previously made the fish extinct
(B) The results of studies measuring the impact on straying rates of habitat loss caused by human activity
(C) The potential for disturbances in one environment to cause the introduction of novel genes into salmon populations in neighboring areas
(D) The weaknesses in the view that the extinction of entire salmon populations is the only mechanism by which human destruction of salmon habitat reduces genetic diversity in salmon
(E) The absence of any reason for believing that disturbances brought about by human activitiy would differ in their effects from comparable disturbances brought about by natural causes

I cannot find any support for option D.
No where in the passage does it say or imply " elimination of entire salmon population is the only way that leads to reduction in genetic diversity"

So the question of weakness in this view does not arise.

I thought answer for this question should be E.

May be I am missing something. Thanks for your help.[/quote]


I'm also having trouble with this one. This is probably wrong but this is the only way I can make the OA fit.

(D) The weaknesses in the view that the extinction of entire salmon populations is the only mechanism by which human destruction of salmon habitat reduces genetic diversity in salmon

what are the weaknesses mentioned?

There is only one as far as I can tell and that is by introducing another possible mechanism by which human destruction of Salmon habitat could reduce genetic diversity. Severe disturbances caused by natural disasters have led to an increase in straying which could limit genetic diversity if as indicated the fish that stray interbreed with the existing stock to such a degree that any local adaptations that are present become diluted. It then goes on to say that environmental disturbances caused by human destruction would likely have the same effect (the reason for the confusion with E.)

So what supports the idea that environmental disturbances caused by human activity could increase straying rates? (D) The fact that environmental disturbances caused by natural disasters have lead to an increase in straying.


(E) The absence of any reason for believing that disturbances brought about by human activity would differ in their effects from comparable disturbances brought about by natural causes

My thinking is that E. might need to be combined with D. for it to be in support and so not correct.

I really hope one of the experts could explain the logic behind this question.[/quote]

E is clearly wrong because disturbances brought by human activity is indeed different from disturbances by natural causes,
D is correct because D says that the following reasoning is wrong: the disturbances by human activity is the only mechanism that eliminates entire population of the fish (in the first paragraph)
C is the trap that I still do not fully understand
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New post 09 Sep 2017, 12:35
Hi Guys,

I found this passage extremely difficult.... Not able to eliminate answer choices for 4 out of 6 questions... And I took almost 14 mintutes of 6 question.

My worry is; what should be a strategy if this passage pops up in actual exam?

Experts : Please suggest.. bb mikemcgarry
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New post 09 Sep 2017, 13:00
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pratik1709 wrote:
Hi Guys,

I found this passage extremely difficult.... Not able to eliminate answer choices for 4 out of 6 questions... And I took almost 14 mintutes of 6 question.

My worry is; what should be a strategy if this passage pops up in actual exam?

Experts : Please suggest.. bb mikemcgarry

Check out the Ultimate RC Guide for Beginners for some tips: https://gmatclub.com/forum/experts-topi ... l#p1857560
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New post 10 Sep 2017, 13:21
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pratik1709 wrote:
Hi Guys,

I found this passage extremely difficult.... Not able to eliminate answer choices for 4 out of 6 questions... And I took almost 14 mintutes of 6 question.

My worry is; what should be a strategy if this passage pops up in actual exam?

Experts : Please suggest.. bb mikemcgarry

Dear pratik1709,

I'm happy to respond. :-)

My friend, please don't bother bb--he's a busy man.

My friend, I think you need to practice reading in general. This is not about an isolated strategy. This is about building your deep understanding of English. See this article:
How to Improve Your GMAT Verbal Score

Does this make sense?
Mike :-)
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Re: Over the last 150 years, large stretches of salmon habitat have been e  [#permalink]

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New post 04 Oct 2017, 22:23
6. Which of the following does the author mention as support for the view that environmental disturbances caused by human activity could increase straying rates?

(A) The existence of salmon populations in rivers where the elimination of salmon habitat by human activity had previously made the fish extinct
(B) The results of studies measuring the impact on straying rates of habitat loss caused by human activity
(C) The potential for disturbances in one environment to cause the introduction of novel genes into salmon populations in neighboring areas
(D) The weaknesses in the view that the extinction of entire salmon populations is the only mechanism by which human destruction of salmon habitat reduces genetic diversity in salmon
(E) The absence of any reason for believing that disturbances brought about by human activitiy would differ in their effects from comparable disturbances brought about by natural causes

Can experts here help me understand the process to reach answer in this one.
I was able to remove only A and ended up selecting C :(
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New post 16 Oct 2017, 04:42
Luckisnoexcuse wrote:
6. Which of the following does the author mention as support for the view that environmental disturbances caused by human activity could increase straying rates?

(A) The existence of salmon populations in rivers where the elimination of salmon habitat by human activity had previously made the fish extinct
(B) The results of studies measuring the impact on straying rates of habitat loss caused by human activity
(C) The potential for disturbances in one environment to cause the introduction of novel genes into salmon populations in neighboring areas
(D) The weaknesses in the view that the extinction of entire salmon populations is the only mechanism by which human destruction of salmon habitat reduces genetic diversity in salmon
(E) The absence of any reason for believing that disturbances brought about by human activitiy would differ in their effects from comparable disturbances brought about by natural causes

Can experts here help me understand the process to reach answer in this one.
I was able to remove only A and ended up selecting C :(


Luckisnoexcuse not an expert but can try to help you with this
I spent a lot of time figuring why otion e is wrong and oprion d is right.
In para 1 author states that""""the numerical effect is obvious: there are fewer salmon in degraded regions than in pristine ones; however, habitat loss also has the potential to reduce genetic diversity. This is most evident in cases where it results in the extinction of entire salmon populations[/color]
Now according to him the habitat loss as well as population loss are both connected to the numerical effect
in the last paragraph author states thatAlthough no one has quantified changes in the rate of straying as a result of the disturbances caused by humans, there is no reason to suspect that the effect would be qualitatively different than what was seen in the aftermath of the Mount Saint Helens eruption.
what does this mean
it means that earlier author was talking about numbers effect on the habitat loss ((( loss of genes))
then he switches to the second paragraph and tells a whole deal about straying and then gives a particular example of Mount Saint Helens eruption. After that he makes an analogy of rate of habitat destruction by comparing the quantified analysis of mount saint Helens eruption mentioned in last lines of second paragraph to yet to be quantified analysis of human destruction of habitat by straying

So, we start the passage beliving that numerical effect is causing the habitat loss, move on to a discussion on straying as habitat loss , give an example, and in final paragraph we compare humans and mount Saint Helens eruptions rate of habitat destructions by straying
option d states that The weaknesses in the view that the extinction of entire salmon populations is the only mechanism by which human destruction of salmon habitat reduces genetic diversity in salmon
You can clearly see the weakness now .The view of numerical effect to consider the loss of habitat.However, its the
straying effect that hasnt been considered ((( yet to be quantified as mentioned in last paragraph)) totally in how humans are destroying loss of habitat
Hope it helps :)
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Re: Over the last 150 years, large stretches of salmon habitat have been e  [#permalink]

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New post 30 Dec 2017, 17:21
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thingocanhnguyen wrote:
Hi all,

The OA of the last question is E. Please help me explain why. Thanks a lot.

This exactly what is described in the last paragraph. There is no reason (i.e. "absence of any reason) to suspect that the effect (i.e. "disturbances brought about by human activity") would be qualitatively different than what was seen in the aftermath of the Mount Saint Helens eruption (i.e. "natural causes").

The preceding paragraph describes and quantifies how the Mount Saint Helens eruption (a natural cause) increased straying rates. Although no one has quantified changes in straying rates caused by human disturbances, there is no reason to believe that the consequences of human disturbances would be much different than the consequences of the eruption (a natural cause).

I hope that helps!
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New post 05 Mar 2018, 04:25
uledssul wrote:
Over the last 150 years, large stretches of salmon habitat have been eliminated by human activity: mining, livestock grazing, timber harvesting, and agriculture as well as recreational and urban development. The numerical effect is obvious: there are fewer salmon in degraded regions than in pristine ones; however, habitat loss also has the potential to reduce genetic diversity. This is most evident in cases where it results in the extinction of entire salmon populations. Indeed, most analysts believe that some kind of environmental degradation underlies the demise of many extinct salmon populations. Although some rivers have been recolonized, the unique genes of the original populations have been lost.

Large-scale disturbances in one locale also have the potential to alter the genetic structure of populations in neighboring areas, even if those areas have pristine habitats. Why? Although the homing instinct of salmon to their natal stream is strong, a fraction of the fish returning from the sea (rarely more than 15 percent) stray and spawn in nearby streams. Low levels of straying are crucial, since the process provides a source of novel genes and a mechanism by which a location can be repopulated should the fish there disappear. Yet high rates of straying can be problematic because misdirected fish may interbreed with the existing stock to such a degree that any local adaptations that are present become diluted. Straying rates remain relatively low when environmental conditions are stable, but can increase dramatically when streams suffer severe disturbance. The 1980 volcanic eruption of Mount Saint Helens, for example, sent mud and debris into several tributaries of the Columbia River. For the next couple of years, steelhead trout (a species included among the salmonids) returning from the sea to spawn were forced to find alternative streams. As a consequence, their rates of straying, initially 16 percent, rose to more than 40 percent overall.

Although no one has quantified changes in the rate of straying as a result of the disturbances caused by humans, there is no reason to suspect that the effect would be qualitatively different than what was seen in the aftermath of the Mount Saint Helens eruption. Such a dramatic increase in straying from damaged areas to more pristine streams results in substantial gene flow, which can in turn lower the overall fitness of subsequent generations.
VRC000460-01
1. The primary purpose of the passage is to

(A) argue against a conventional explanation for the extinction of certain salmon populations and suggest an alternative
(B) correct a common misunderstanding about the behavior of salmon in response to environmental degradation caused by human activity
(C) compare the effects of human activity on salmon populations with the effects of natural disturbances on salmon populations
(D) differentiate the particular effects of various human activities on salmon habitats
(E) describe how environmental degradation can cause changes in salmon populations that extend beyond a numerical reduction




VRC000460-02
2. It can be inferred from the passage that the occasional failure of some salmon to return to their natal streams in order to spawn provides a mechanism by which

(A) pristine streams that are near polluted streams become polluted themselves
(B) the particular adaptations of a polluted stream’s salmon population can be preserved without dilution
(C) the number of salmon in pristine habitats decreases relative to the number in polluted streams
(D) an environmentally degraded stream could be recolonized by new salmon populations should the stream recover
(E) the extinction of the salmon populations that spawn in polluted streams is accelerated




VRC000460-03
3. According to the passage, human activity has had which of the following effects on salmon populations?

(A) An increase in the size of salmon populations in some previously polluted rivers
(B) A decline in the number of salmon in some rivers
(C) A decrease in the number straying salmon in some rivers
(D) A decrease in the gene flow between salmon populations that spawn in polluted streams and populations that spawn in pristine streams
(E) A decline in the vulnerability of some salmon populations to the effects of naturally occurring habitat destruction




4. The author mentions the “aftermath of the Mount Saint Helens eruption” most likely in order to

(A) provide an example of the process that allows the repopulation of rivers whose indigenous salmon population has become extinct
(B) indicate the extent to which the disturbance of salmon habitat by human activity in one stream might affect the genetic structure of salmon populations elsewhere
(C) provide a standard of comparison against which the impact of human activity on the gene flow among salmon populations should be measured
(D) show how salmons’ homing instinct can be impaired as a result of severe environmental degradation of their natal streams
(E) show why straying rates in salmon populations remain generally low except when spawning streams suffer severe environmental disturbance




VRC000460-05
5. The author's argument that increased straying can "lower the overall fitness of subsequent generations" (see hightlited text) is based on which of the following assumptions?

(A) A disturbance of salmonid spawning streams caused by human activity could increase the straying rate of affected salmonid populations as much as the aftermath of the Mount Saint Helens eruption did.
(B) In the streams in which the straying salmonids spawn, these straying salmonids would amount to no more than 40 percent of the total spawning population
(C) Salmonids in some streams benefit from particular local adaptions.
(D) Nonenvironmental factors have no effect on salmonid straying rates.
(E) At least some of the streams in which straying salmonids would spawn are pristine, affected by neither natural nor artificial disturbances.




VRC000460-07
6. Which of the following does the author mention as support for the view that environmental disturbances caused by human activity could increase straying rates?

(A) The existence of salmon populations in rivers where the elimination of salmon habitat by human activity had previously made the fish extinct
(B) The results of studies measuring the impact on straying rates of habitat loss caused by human activity
(C) The potential for disturbances in one environment to cause the introduction of novel genes into salmon populations in neighboring areas
(D) The weaknesses in the view that the extinction of entire salmon populations is the only mechanism by which human destruction of salmon habitat reduces genetic diversity in salmon
(E) The absence of any reason for believing that disturbances brought about by human activitiy would differ in their effects from comparable disturbances brought about by natural causes




-----------------------------------------------------------------------------------------------------------------

Hi mikemcgarry

Please explain Q2,4,5 and 6. I ended up marking these wrong.

Thanks,

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New post 08 Mar 2018, 17:27
ucb2k7 wrote:
Hi mikemcgarry ,

can you please explain Q2,4,5 and 6 for the passage.

ucb2k7, this is certainly a challenging passage, but can you try explaining your selections for the questions that you asked about? Sometimes, attempting to explain your thought process can lead you to the correct answer. Also, I know that the always-amazing mikemcgarry (Hi Mike!) receives numerous requests for help every day, and I imagine that he'd give priority to questions that are a bit more specific and thoughtful. The more information you provide, the easier it is for all of us to help!

As discussed in our RC Guide for Beginners, try reading the passage again and focusing on structure and purpose, rather than worrying about every little detail:

Quote:
Here’s the basic structure that we recommend: stop at the end of each paragraph, and ask yourself WHY the author has written the paragraph. Your focus should be on the big picture: each paragraph’s purpose and how each paragraph connects with the previous paragraphs. If you’re crystal-clear about WHY the author has written every paragraph – and how they fit together – you’ll be in great shape for the contextual questions that you’ll inevitably see next.

See if that approach helps improve your understanding of the passage, and then give the questions another shot. Then, as I recommended above, try explaining your thought process for the ones that you miss.

Question #4 does not appear to be from the GMAT Official Practice questions, so I wouldn't worry about that one.

Good luck!
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Re: Over the last 150 years, large stretches of salmon habitat have been e  [#permalink]

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New post 09 Mar 2018, 14:17
1
ucb2k7 wrote:
uledssul wrote:
Over the last 150 years, large stretches of salmon habitat have been eliminated by human activity: mining, livestock grazing, timber harvesting, and agriculture as well as recreational and urban development. The numerical effect is obvious: there are fewer salmon in degraded regions than in pristine ones; however, habitat loss also has the potential to reduce genetic diversity. This is most evident in cases where it results in the extinction of entire salmon populations. Indeed, most analysts believe that some kind of environmental degradation underlies the demise of many extinct salmon populations. Although some rivers have been recolonized, the unique genes of the original populations have been lost.

Large-scale disturbances in one locale also have the potential to alter the genetic structure of populations in neighboring areas, even if those areas have pristine habitats. Why? Although the homing instinct of salmon to their natal stream is strong, a fraction of the fish returning from the sea (rarely more than 15 percent) stray and spawn in nearby streams. Low levels of straying are crucial, since the process provides a source of novel genes and a mechanism by which a location can be repopulated should the fish there disappear. Yet high rates of straying can be problematic because misdirected fish may interbreed with the existing stock to such a degree that any local adaptations that are present become diluted. Straying rates remain relatively low when environmental conditions are stable, but can increase dramatically when streams suffer severe disturbance. The 1980 volcanic eruption of Mount Saint Helens, for example, sent mud and debris into several tributaries of the Columbia River. For the next couple of years, steelhead trout (a species included among the salmonids) returning from the sea to spawn were forced to find alternative streams. As a consequence, their rates of straying, initially 16 percent, rose to more than 40 percent overall.

Although no one has quantified changes in the rate of straying as a result of the disturbances caused by humans, there is no reason to suspect that the effect would be qualitatively different than what was seen in the aftermath of the Mount Saint Helens eruption. Such a dramatic increase in straying from damaged areas to more pristine streams results in substantial gene flow, which can in turn lower the overall fitness of subsequent generations.
VRC000460-01
1. The primary purpose of the passage is to

(A) argue against a conventional explanation for the extinction of certain salmon populations and suggest an alternative
(B) correct a common misunderstanding about the behavior of salmon in response to environmental degradation caused by human activity
(C) compare the effects of human activity on salmon populations with the effects of natural disturbances on salmon populations
(D) differentiate the particular effects of various human activities on salmon habitats
(E) describe how environmental degradation can cause changes in salmon populations that extend beyond a numerical reduction




VRC000460-02
2. It can be inferred from the passage that the occasional failure of some salmon to return to their natal streams in order to spawn provides a mechanism by which

(A) pristine streams that are near polluted streams become polluted themselves
(B) the particular adaptations of a polluted stream’s salmon population can be preserved without dilution
(C) the number of salmon in pristine habitats decreases relative to the number in polluted streams
(D) an environmentally degraded stream could be recolonized by new salmon populations should the stream recover
(E) the extinction of the salmon populations that spawn in polluted streams is accelerated




VRC000460-03
3. According to the passage, human activity has had which of the following effects on salmon populations?

(A) An increase in the size of salmon populations in some previously polluted rivers
(B) A decline in the number of salmon in some rivers
(C) A decrease in the number straying salmon in some rivers
(D) A decrease in the gene flow between salmon populations that spawn in polluted streams and populations that spawn in pristine streams
(E) A decline in the vulnerability of some salmon populations to the effects of naturally occurring habitat destruction




4. The author mentions the “aftermath of the Mount Saint Helens eruption” most likely in order to

(A) provide an example of the process that allows the repopulation of rivers whose indigenous salmon population has become extinct
(B) indicate the extent to which the disturbance of salmon habitat by human activity in one stream might affect the genetic structure of salmon populations elsewhere
(C) provide a standard of comparison against which the impact of human activity on the gene flow among salmon populations should be measured
(D) show how salmons’ homing instinct can be impaired as a result of severe environmental degradation of their natal streams
(E) show why straying rates in salmon populations remain generally low except when spawning streams suffer severe environmental disturbance




VRC000460-05
5. The author's argument that increased straying can "lower the overall fitness of subsequent generations" (see hightlited text) is based on which of the following assumptions?

(A) A disturbance of salmonid spawning streams caused by human activity could increase the straying rate of affected salmonid populations as much as the aftermath of the Mount Saint Helens eruption did.
(B) In the streams in which the straying salmonids spawn, these straying salmonids would amount to no more than 40 percent of the total spawning population
(C) Salmonids in some streams benefit from particular local adaptions.
(D) Nonenvironmental factors have no effect on salmonid straying rates.
(E) At least some of the streams in which straying salmonids would spawn are pristine, affected by neither natural nor artificial disturbances.




VRC000460-07
6. Which of the following does the author mention as support for the view that environmental disturbances caused by human activity could increase straying rates?

(A) The existence of salmon populations in rivers where the elimination of salmon habitat by human activity had previously made the fish extinct
(B) The results of studies measuring the impact on straying rates of habitat loss caused by human activity
(C) The potential for disturbances in one environment to cause the introduction of novel genes into salmon populations in neighboring areas
(D) The weaknesses in the view that the extinction of entire salmon populations is the only mechanism by which human destruction of salmon habitat reduces genetic diversity in salmon
(E) The absence of any reason for believing that disturbances brought about by human activitiy would differ in their effects from comparable disturbances brought about by natural causes




-----------------------------------------------------------------------------------------------------------------

Hi mikemcgarry

Please explain Q2,4,5 and 6. I ended up marking these wrong.

Thanks,

ucb2k7


Hi ucb2k7!

Carolyn from Magoosh here :-) Mike can't respond right now, but I'd be happy to answer your questions :-) However, as GMATNinja mentioned, it would be really useful if you could make your questions a bit more specific. Please try to explain your thought process for each question, and mention what exactly you're having trouble understanding. That way we can provide better, more specific explanations!

Thanks! :-)
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Re: Over the last 150 years, large stretches of salmon habitat have been e  [#permalink]

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New post 20 Jun 2018, 04:22
mikemcgarry wrote:
voodoochild wrote:
It can be inferred from the passage that the occasional failure of some salmon to return to their natal streams in order to spawn provides a mechanism by which
a. pristine streams that are near polluted streams become polluted themselves
b. the particular adaptations of a polluted stream’s salmon population can be preserved without dilution
c. the number of salmon in pristine habitats decreases relative to the number in polluted streams
d. an environmentally degraded stream could be recolonized by new salmon populations should the stream recover
e. the extinction of the salmon populations that spawn in polluted streams is accelerated


OA D

Why is B wrong? When high straying happens, dilution is the issue. Hence, when low straying happens, dilution is not an issue at all -- what B) says. Also lines (30), " Low levels of straying are crucial, since the process provides a source of novel genes and a mechanism by which a location can be (40) repopulated should the fish there disappear. " --- implies genes are preserved -- and as the next sentence says "dilution happens" in case of high straying. Can't we infer that in case of low straying, no dilution happens and the genes are preserved?

B is quite wrong because the passage makes very clear --- when a stream is polluted, straying happens, which means dilution happens. The passage describes clearly the straying that resulted from the Mount St. Helen's eruption, and then around line (70) says that the effect of pollution probably would be about the same as what they saw at Mount St. Helen's. When the stream is polluted, the salmon can't use it to spawn, so they stray.

voodoochild wrote:
The author's argument that increased straying can "lower the overall fitness of subsequent generation" (see highlighted text) is based on which of the following assumptions?
a) a disturbance of salmonid spawning streams caused by human activtity will increasing the straying rate of affected salmonid populations as much as the aftermath of the Mount Saint Helens eruption did.
b) In the streams in which the straying salmonids spawn, these straying salmonids would amount to no more than 40 percent of total spawning population
c) Salmonids in some streams benefit from particular local adaptations
d) Nonenvironmental factors have no effect
e) At least some of the streams in which straying salmonids would spawn are pristine, affected by neither natural nor artificial disturbances.


OA C


Why is E) wrong? Also what support do we have for C) To me, "lowering the overall fitness" implies less likely to pass Darwin's "survival of the fittest" Hence, such adaptations are in fact bad -- 180 to what the OA is :( To me, the conclusion is that straying because of human effects causes bad things to Salmon in pristine streams. What's the support? Straying causing the dilution of the gene pool. I couldn't find that answer choice.

You're correct in your understanding of "fitness" --- we are talking about Darwinian fitness here.

The passage says "high rates of straying can be problematic because misdirected fish may interbreed with the existing stock to such a degree that any local adaptations that are present become diluted." In other words, the salmon in those pristine areas had adaptions particular suited to those areas, which made them quite fit, and along come a bunch of salmon from the polluted stream next door, and they genetically dilute the salmon of that pristine stream, making them less adapted to that unique niche, and hence less fit. That passage is enormous support for (C)

(E) is a typically GMAT RC distractor, and you fell for the bait. It is a statement that's true in general, but not relevant to the argument. Suppose we said that there was no such thing as a "pristine" perfect place for salmon --- suppose even the environments with zero pollution had natural challenges. Well, then, the salmon in those environments, over the centuries, would adapt to those particular conditions and be quite fit, and then if others stray into their unique stream and interbreed with them, it will reduce the fitness of that population.

Does all this make sense?

Mike :-)





Hi Mike,

Could you please explain why the correct option is C and not E for the below question.

4. The author mentions the “aftermath of the Mount Saint Helens eruption” most likely in order to

(A) provide an example of the process that allows the repopulation of rivers whose indigenous salmon population has become extinct
(B) indicate the extent to which the disturbance of salmon habitat by human activity in one stream might affect the genetic structure of salmon populations elsewhere
(C) provide a standard of comparison against which the impact of human activity on the gene flow among salmon populations should be measured
(D) show how salmons’ homing instinct can be impaired as a result of severe environmental degradation of their natal streams
(E) show why straying rates in salmon populations remain generally low except when spawning streams suffer severe environmental disturbance
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Re: Over the last 150 years, large stretches of salmon habitat have been e   [#permalink] 20 Jun 2018, 04:22

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