In a polluted area around the Great Lakes, scientists : GMAT Critical Reasoning (CR)
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# In a polluted area around the Great Lakes, scientists

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In a polluted area around the Great Lakes, scientists [#permalink]

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29 Dec 2012, 23:01
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84% (02:04) correct 16% (00:59) wrong based on 90 sessions

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In a polluted area around the Great Lakes, scientists studying bird populations have observed a drop in the number of both herring gulls and terns. Both bird species prey on the same type of fish, whose numbers are also being negatively affected by pollution. However, the tern population has seen a much sharper decrease than the herring gull population. Scientists have concluded that the herring gulls have a higher survival rate because they are able to find alternative sources of food, including garbage dumps along the shoreline.

Which of the following, if true, would provide the best piece of evidence in support of the researchers' conclusion?

A) A survey shows that bird populations in areas around the Great Lakes have shown similar decreases.
B)A related study finds that fish populations in the Great Lakes are affected as much by other predators as by pollution.
C) Maps of the area reveal that the largest garbage dump in the area is located 3 miles inland from the lake.
D) Blood tests performed on the gulls reveal high levels of the types of fatty acids generally found only in human food.
E)Analysis of water in the area where the birds nest reveals that toxin levels are actually slightly below fish tolerance levels.

Why 'D' and Why not 'C' ?
[Reveal] Spoiler: OA

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Re: In a polluted area around the Great Lakes, scientists [#permalink]

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29 Dec 2012, 23:28
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This question requires a piece of evidence to support scientist's conclusion - Herring gulls have a higher survival rate because they are able to find alternative sources of food. The evidence can be in any applicable form which proves Gulls have actually ate something from alternative source of food, e.g. a scientific test on Gulls or people sighting a flock of gulls sitting on garbage dumps eating leftovers.

A) A survey shows that bird populations in areas around the Great Lakes have shown similar decreases.
-- outside of scope
B)A related study finds that fish populations in the Great Lakes are affected as much by other predators as by pollution.
-- Irrelevant for conclusion
C) Maps of the area reveal that the largest garbage dump in the area is located 3 miles inland from the lake.
-- It does not support the conclusion. Stating the presence of garbage dump near lake does not prove whether gulls are feeding from the garbage as their alternative source. Hence this choice is incorrect due to lack of evidence.
D) Blood tests performed on the gulls reveal high levels of the types of fatty acids generally found only in human food.
-- Correct! These tests reveal that Gull's blood contains the fatty acids generally found ONLY in human food, hence those gulls must be feeding from garbage dumps or other source of human foods.
E)Analysis of water in the area where the birds nest reveals that toxin levels are actually slightly below fish tolerance levels.
-- This does not provide any evidence to support the conclusion.
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Re: In a polluted area around the Great Lakes, scientists [#permalink]

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29 Dec 2012, 23:35
Aristocrat wrote:
In a polluted area around the Great Lakes, scientists studying bird populations have observed a drop in the number of both herring gulls and terns. Both bird species prey on the same type of fish, whose numbers are also being negatively affected by pollution. However, the tern population has seen a much sharper decrease than the herring gull population. Scientists have concluded that the herring gulls have a higher survival rate because they are able to find alternative sources of food, including garbage dumps along the shoreline.

Which of the following, if true, would provide the best piece of evidence in support of the researchers' conclusion?

A) A survey shows that bird populations in areas around the Great Lakes have shown similar decreases.
B)A related study finds that fish populations in the Great Lakes are affected as much by other predators as by pollution.
C) Maps of the area reveal that the largest garbage dump in the area is located 3 miles inland from the lake.
D) Blood tests performed on the gulls reveal high levels of the types of fatty acids generally found only in human food.
E)Analysis of water in the area where the birds nest reveals that toxin levels are actually slightly below fish tolerance levels.

Why 'D' and Why not 'C' ?

Hi Aristocrat,

Compare the two choices which are two contenders for strengthening the conclusion

C) Maps of the area reveal that the largest garbage dump in the area is located 3 miles inland from the lake.

Map is a hard evidence that says the largest garbage dump in the area is located 3 miles inland from the lake. which indirectly refutes the premise that herring gulls have a higher survival rate because they are able to find alternative sources of food, including garbage dumps along the shoreline.

And as premise is taken by its words, we cannot the refute the same.

whereas

D) Blood tests performed on the gulls reveal high levels of the types of fatty acids generally found only in human food.

Strengthens the arg. conlcusion that the birds are getting their food from the waste irrespective of what the source of the food is.

Pls let me know if i'm missing a pt here.

Thanks
Manager
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GMAT Date: 11-18-2012
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Re: In a polluted area around the Great Lakes, scientists [#permalink]

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29 Dec 2012, 23:51
How can we claim that
garbage dump contains mostly of food waste consumed by human.
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Re: In a polluted area around the Great Lakes, scientists [#permalink]

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29 Dec 2012, 23:53
jsahni123 wrote:
Aristocrat wrote:
In a polluted area around the Great Lakes, scientists studying bird populations have observed a drop in the number of both herring gulls and terns. Both bird species prey on the same type of fish, whose numbers are also being negatively affected by pollution. However, the tern population has seen a much sharper decrease than the herring gull population. Scientists have concluded that the herring gulls have a higher survival rate because they are able to find alternative sources of food, including garbage dumps along the shoreline.

Which of the following, if true, would provide the best piece of evidence in support of the researchers' conclusion?

A) A survey shows that bird populations in areas around the Great Lakes have shown similar decreases.
B)A related study finds that fish populations in the Great Lakes are affected as much by other predators as by pollution.
C) Maps of the area reveal that the largest garbage dump in the area is located 3 miles inland from the lake.
D) Blood tests performed on the gulls reveal high levels of the types of fatty acids generally found only in human food.
E)Analysis of water in the area where the birds nest reveals that toxin levels are actually slightly below fish tolerance levels.

Why 'D' and Why not 'C' ?

Hi Aristocrat,

Compare the two choices which are two contenders for strengthening the conclusion

C) Maps of the area reveal that the largest garbage dump in the area is located 3 miles inland from the lake.

Map is a hard evidence that says the largest garbage dump in the area is located 3 miles inland from the lake. which indirectly refutes the premise that herring gulls have a higher survival rate because they are able to find alternative sources of food, including garbage dumps along the shoreline.

And as premise is taken by its words, we cannot the refute the same.

whereas

D) Blood tests performed on the gulls reveal high levels of the types of fatty acids generally found only in human food.

Strengthens the arg. conlcusion that the birds are getting their food from the waste irrespective of what the source of the food is.

Pls let me know if i'm missing a pt here.

Thanks

How 'C' refutes an argument.
it may be supporting that because of close proximity of garbage dump.
birds might be feeding on them.
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Re: In a polluted area around the Great Lakes, scientists [#permalink]

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30 Dec 2012, 00:06
Aristocrat wrote:
How can we claim that
garbage dump contains mostly of food waste consumed by human.

My explanation above mentions "garbage dumps or other source of human foods", since the evidence from gull's blood test proves the presence of fatty acids generally found only in human food.

The main argument does not limit its claim to Garbage dumps as the only source. It states "they are able to find alternative sources of food, including garbage dumps along the shoreline". That means Gulls might be also feeding from other alternative sources of food. Hence our objective to show evidence that Gulls are feeding from alternate source of food (other than their primary source fish), whether its garbage dumps or alternate sources such as human food.
_________________

Thanks,
Prashant Ponde

Tough 700+ Level RCs: Passage1 | Passage2 | Passage3 | Passage4 | Passage5 | Passage6 | Passage7
Reading Comprehension notes: Click here
VOTE GMAT Practice Tests: Vote Here
PowerScore CR Bible - Official Guide 13 Questions Set Mapped: Click here
Looking to finance your tuition: Click here

Intern
Status: Winning is not everything, but wanting to win is
Joined: 10 Nov 2010
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WE 1: IT Consultant (6Yr)
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Kudos [?]: 9 [0], given: 5

Re: In a polluted area around the Great Lakes, scientists [#permalink]

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30 Dec 2012, 01:21
Aristocrat wrote:
jsahni123 wrote:
Aristocrat wrote:
In a polluted area around the Great Lakes, scientists studying bird populations have observed a drop in the number of both herring gulls and terns. Both bird species prey on the same type of fish, whose numbers are also being negatively affected by pollution. However, the tern population has seen a much sharper decrease than the herring gull population. Scientists have concluded that the herring gulls have a higher survival rate because they are able to find alternative sources of food, including garbage dumps along the shoreline.

Which of the following, if true, would provide the best piece of evidence in support of the researchers' conclusion?

A) A survey shows that bird populations in areas around the Great Lakes have shown similar decreases.
B)A related study finds that fish populations in the Great Lakes are affected as much by other predators as by pollution.
C) Maps of the area reveal that the largest garbage dump in the area is located 3 miles inland from the lake.
D) Blood tests performed on the gulls reveal high levels of the types of fatty acids generally found only in human food.
E)Analysis of water in the area where the birds nest reveals that toxin levels are actually slightly below fish tolerance levels.

Why 'D' and Why not 'C' ?

Hi Aristocrat,

Compare the two choices which are two contenders for strengthening the conclusion

C) Maps of the area reveal that the largest garbage dump in the area is located 3 miles inland from the lake.

Map is a hard evidence that says the largest garbage dump in the area is located 3 miles inland from the lake. which indirectly refutes the premise that herring gulls have a higher survival rate because they are able to find alternative sources of food, including garbage dumps along the shoreline.

And as premise is taken by its words, we cannot the refute the same.

whereas

D) Blood tests performed on the gulls reveal high levels of the types of fatty acids generally found only in human food.

Strengthens the arg. conlcusion that the birds are getting their food from the waste irrespective of what the source of the food is.

Pls let me know if i'm missing a pt here.

Thanks

How 'C' refutes an argument.
it may be supporting that because of close proximity of garbage dump.
birds might be feeding on them.

Hi Aristocrat,

I'll focus here on the main pt of the argument.Pls let me know if i'm incorrect here.

Premise : Because they (gulls) are able to find alternative sources of food, including garbage dumps along the shoreline.

Conclusion : Scientists have concluded that the herring gulls have a higher survival rate

Assumption: Food found from alternative source/garbage dump is consumable by birds leading to higher survival rate.

Hence D strengthens the arg. saying that "Blood tests performed on the gulls reveal high levels of the types of fatty acids generally found only in human food."

As per my understanding considering the factor of location is out of scope here.

Also C says that garbage dump is 3 miles inside.

As it involves assuming that whether the distance of 3 miles is near or farther. Hence it could be refuting/strengthening the argument depending upon the assumption under consideration.

Thanks
Jatin
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Re: In a polluted area around the Great Lakes, scientists [#permalink]

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23 Jul 2014, 04:09
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Re: In a polluted area around the Great Lakes, scientists [#permalink]

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03 Nov 2015, 19:48
Hello from the GMAT Club VerbalBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

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Re: In a polluted area around the Great Lakes, scientists   [#permalink] 03 Nov 2015, 19:48
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