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# To prevent a newly built dam on the Chiff River

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Joined: 16 Oct 2010
Posts: 8132
Location: Pune, India
Re: To prevent a newly built dam on the Chiff River  [#permalink]

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10 Sep 2017, 21:50
1
rippen3 wrote:
VeritasPrepKarishma wrote:
dgr8sandeep wrote:
(A) Fish that have migrated to the upstream breeding grounds do not return down the Chiff River again.
Irrelevant. What happens to them after the migrate, we don't care. We want to know why they are not migrating.

(B) On other rivers in the region, the construction of dams with fish passes has led to only small decreases in the number of fish migrating upstream.
This strengthens that our fish pass is defective! At other places, the decrease is less. We are seeing a huge decrease.

(C) The construction of the dam stirred up potentially toxic river sediments that were carried downstream.
This provides us a reason why fewer fish are swimming upriver. Perhaps because there are fewer fish now. The construction introduced toxic substances in the river which should have killed many fish. Hence, the fish pass may not be faulty. The problem may be that we have fewer fish now.
Correct.

(D) Populations of migratory fish in the Chiff River have been declining slightly over the last 20 years.
The population has been declining slightly over many years. It doesn't explain the huge decrease in the number of fish swimming upriver.

(E) During spawning season, the dam releases sufficient water far migratory fish below the dam to swim upstream.
The dam is aiding the fish by providing enough water for them to swim upstream. So the fewer fish swimming upstream would not be expected. Hence defective fish pass could actually be the reason.

Thank you for your illustrations. I chose A because, when it says these fish are not returning, this offers an explanation that the population of the downstream only decreases, thus making a possibility why only 300 fish made it through the gate(300 fish may be a good level after this population decrease). Is there anything not appropriate with this logic?

The argument tells us that there is a season in which fish migrate upstream. In every migration season, 1000 fish were migrating upstream every day. In the first season after the construction of the dam, only 300 fish migrated every day.

Option (A) uses simple present to tell us a fact: Once the fish migrate, they don't come back down.
This was true in every season before the dam was made. Still 1000 fish were migrating every season. Only this season 300 fish are migrating. So option (A) doesn't explain why the fish pass may be ok.
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Re: To prevent a newly built dam on the Chiff River  [#permalink]

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28 Mar 2018, 19:57
zoezhuyan wrote:
zoezhuyan wrote:
Hi mikemcgarry

I am afraid I need you help

To prevent a newly built dam on the Chiff River from blocking the route of fish migrating to breeding grounds upstream, the dam includes a fish pass, a mechanism designed to allow fish through the dam. Before the construction of the dam and fish pass, several thousand fish a day swam upriver during spawning season. But in the first season after the project's completion, only 300 per day made the journey. Clearly, the fish pass is defective.

Which of the following, if true, most seriously weakens the argument?

(A) Fish that have migrated to the upstream breeding grounds do not return down the Chiff River again.
(B) On other rivers in the region, the construction of dams with fish passes has led to only small decreases in the number of fish migrating upstream.
(C) The construction of the dam stirred up potentially toxic river sediments that were carried downstream.
(D) Populations of migratory fish in the Chiff River have been declining slightly over the last 20 years.
(E) During spawning season, the dam releases sufficient water far migratory fish below the dam to swim upstream
.

I picked up E, because,
in the prompt, it states thousands fish swam a per day during spawning season, but in the first season only 300 per day swam, the decreased number is between different seasons.
While choice E states that dam release sufficient water in spawning season, hmmm, E points out a reason, sufficient water from dam, that thousands fish swam, I can get the reason that no sufficient water in the first season after building dam, leading few fish swam,
in other words, it eliminates the factor -- fish pass defective,

Have a nice day

>_~

Hi mikemcgarry, GMATNinjaTwo, GMATNinja, MagooshExpert Carolyn, sayantanc2k,

(E) certainly eliminates a problem with the dam, not with the fish pass. In other words, if the dam did NOT release sufficient water, then we would see a decrease in fish migrating upstream EVEN IF the fish pass is totally fine. So (E) eliminates an alternative explanation (problem with the dam itself). If anything, this supports the notion that there might be a problem with the fish pass.

(C), on the other hand, gives a reason why the fish population would have been reduced. This population decrease could explain the decrease in the number that swam upstream. By providing an alternate explanation, (C) weakens the argument.

I hope that helps!
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Re: To prevent a newly built dam on the Chiff River  [#permalink]

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28 Mar 2018, 21:43
GMATNinja wrote:
(E) certainly eliminates a problem with the dam, not with the fish pass. In other words, if the dam did NOT release sufficient water, then we would see a decrease in fish migrating upstream EVEN IF the fish pass is totally fine. So (E) eliminates an alternative explanation (problem with the dam itself). If anything, this supports the notion that there might be a problem with the fish pass.

(C), on the other hand, gives a reason why the fish population would have been reduced. This population decrease could explain the decrease in the number that swam upstream. By providing an alternate explanation, (C) weakens the argument.

I hope that helps!

Thanks GMATNinja

it is easy to lost when I practice verb questions, especially CR

Have a nice day
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Joined: 14 Feb 2016
Posts: 36
Re: To prevent a newly built dam on the Chiff River  [#permalink]

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17 Apr 2018, 01:57
To prevent a newly built dam on the Chiff River from blocking the route of fish migrating to breeding grounds upstream, the dam includes a fish pass, a mechanism designed to allow fish through the dam. Before the construction of the dam and fish pass, several thousand fish a day swam upriver during spawning season. But in the first season after the project's completion, only 300 per day made the journey. Clearly, the fish pass is defective.

Which of the following, if true, most seriously weakens the argument?
(A) Fish that have migrated to the upstream breeding grounds do not return down the Chiff River again.
(B) On other rivers in the region, the construction of dams with fish passes has led to only small decreases in the number of fish migrating upstream.
(C) The construction of the dam stirred up potentially toxic river sediments that were carried downstream.
(D) Populations of migratory fish in the Chiff River have been declining slightly over the last 20 years.
(E) During spawning season, the dam releases sufficient water for migratory fish below the dam to swim upstream.
Review using the CR Bible:

Conclusion: The fish pass is defective.

Premise: Before the construction of the dam and fish pass, thousand fish a day swam upriver. But in the first season after the project’s completion, only 300 per day made the journey.

Weakening scenario: The author relies on incomplete evidence, it is unclear whether the construction of the fish pass is the sole reason for a decrease in fish swimming upriver.

Prephrase: The correct answer choice would a) disprove the premise, b) show another reason for the decrease of fish swimming through and c) provide alternative evidence that the fish pass is working.

Answer choice A: this answer choice is designed to confuse us. It might mean that the fish pass is defective because it doesn’t let anyone return. But how did they get there in the first place?. The fact that the fish don’ t get back from the journey doesn’t change anything about the fact that the fish can make the journey in the first place. This answer is therefore slightly out of scope.

Answer choice B: This actually strengthens the argument by proving that building the dam leads to a decrease. Opposite answer.

Answer choice C: This provides direct evidence for an alternate reason that the fish don’t swim through. The toxins released might kill the fish. So the culprit isn’t the dam, but the toxins! CONTENDER.

Answer choice D: Declining slightly. Okay – but slightly isn’t 70% of the fish less. This answer choice demonstrates how important it is to exactly analyze words such as slightly, probably etc.

Answer choice E: Ok. This might mean that the dam is working. But it is only during spawning season. So… What about the other seasons? Get out of here with and mislead someone else
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Re: To prevent a newly built dam on the Chiff River &nbs [#permalink] 17 Apr 2018, 01:57

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