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Two decades after the Emerald River Dam was built, none of

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Two decades after the Emerald River Dam was built, none of [#permalink] New post 03 May 2010, 13:15
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Official Guide for GMAT Verbal Review, 2nd Edition

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Question No.: 35
Page: 129
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Two decades after the Emerald River Dam was built, none of the eight fish species native to the Emerald River was still reproducing adequately in the river below the dam. Since the dam reduced the annual range of water temperature in the river below the dam from 50 degrees to 6 degrees, scientists have hypothesized that sharply rising water temperatures must be involved in signaling the native species to begin the reproductive cycle.

Which of the following statements, if true, would most strengthen the scientists’ hypothesis?
(A) The native fish species were still able to reproduce only in side streams of the river below the dam where the annual temperature range remains approximately 50 degrees.
(B) Before the dam was built, the Emerald River annually overflowed its banks, creating backwaters that were critical breeding areas for the native species of fish.
(C) The lowest recorded temperature of the Emerald River before the dam was built was 34 degrees, whereas the lowest recorded temperature of the river after the dam was built has been 43 degrees.
(D) Nonnative species of fish, introduced into the Emerald River after the dam was built, have begun competing with the declining native fish species for food and space.
(E) Five of the fish species native to the Emerald River are not native to any other river in North America.
[Reveal] Spoiler: OA

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Re: Emerald River Dam [#permalink] New post 03 May 2010, 19:42
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A. A says that the SAME species of fish are reproducing ~50degrees while the passage suggests the same species are not reproducing under the dam with temperature at 6 degrees. so raising the temperature up should get some reproduction going.
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Re: Emerald River Dam [#permalink] New post 03 May 2010, 21:21
IMO A.

Premise - Decrease in temp >>> decline in fish population
Conclusion - Rise in temp causes fishes to reproduce.

Let'c check choices:
(A) The native fish species were still able to reproduce only in side streams of the river below the dam where the annual temperature range remains approximately 50 degrees. [Correct. ]

(B) Before the dam was built, the Emerald River annually overflowed its banks, creating backwaters that were critical breeding areas for the native species of fish. [This is OUT OF SCOPE. Incorrect]

(C) The lowest recorded temperature of the Emerald River before the dam was built was 34 degrees, whereas the lowest recorded temperature of the river after the dam was built has been 43 degrees. [This is not showing the temp decrease or temp increase and also reverse to one of the facts - Since the dam reduced the annual range of water temperature in the river below the dam from 50 degrees to 6 degrees. Incorrect]

(D) Nonnative species of fish, introduced into the Emerald River after the dam was built, have begun competing with the declining native fish species for food and space. [Simply a Weaking. It is against scientists' hypothesis. Incorrect]

(E) Five of the fish species native to the Emerald River are not native to any other river in North America. [We dont know how many species. This choice is OUT of SCOPE. Incorrect]

noboru wrote:
Two decades after the Emerald River Dam was built, none of the eight fish species native to the Emerald River was still reproducing adequately in the river below the dam. Since the dam reduced the annual range of water temperature in the river below the dam from 50 degrees to 6 degrees, scientists have hypothesized that sharply rising water temperatures must be involved in signaling the native species to begin the reproductive cycle.

Which of the following statements, if true, would most strengthen the scientists’ hypothesis?
(A) The native fish species were still able to reproduce only in side streams of the river below the dam where the annual temperature range remains approximately 50 degrees.
(B) Before the dam was built, the Emerald River annually overflowed its banks, creating backwaters that were critical breeding areas for the native species of fish.
(C) The lowest recorded temperature of the Emerald River before the dam was built was 34 degrees, whereas the lowest recorded temperature of the river after the dam was built has been 43 degrees.
(D) Nonnative species of fish, introduced into the Emerald River after the dam was built, have begun competing with the declining native fish species for food and space.
(E) Five of the fish species native to the Emerald River are not native to any other river in North America.

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Re: Emerald River Dam [#permalink] New post 10 Jan 2011, 11:21
I WONDER IF THE TEMP. ACTUALLY DECREASES OR THE RANGE OF TEMP DOES. TRICKY QUESTION.
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Re: Emerald River Dam [#permalink] New post 05 Mar 2011, 12:03
IMO C. the scientists say SHARP RISE in temperature. this can happen only when there is a vast difference between the highest and lowest. best explained by C
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Re: Two decades after the Emerald River Dam was built, none of [#permalink] New post 21 Mar 2012, 18:14
I picked the answer A:

The conclusion is: [highlight]Scientists have hypothesized that sharply rising water temperatures must be involved in signaling the native species to begin the reproductive cycle.[/highlight]

A. This presents a strong reason to support their hypothesis. You are essentially performing a sensitivity test - you are just changing the temperature range and seeing how the fish react. All the other variables have been kept constant (ie. same fish, same river etc.). Therefore, if the same fish can reproduce in the same river with only a change in the temperature range, that is proof that the dam has changed the reproductive cycle.

B. First, I believe that this point is irrelevant because we are only concerned about the relationship between reproductive cycle in the river below the dam and the temperature of the river. Also, this answer choice could potentially point to another reason why reproductive cycles happened before the dam was built - in this case it would weaken the argument. In either case, this answer is incorrect.

C. This answer choice only gives you 2 specific temperatures. The first question I had was "where were temperatures recorded?" There is no explanation of that in this answer choice, so the temperature readings could actually have been taken before the dam - that would be irrelevant to this question since we are only concerned with the river after the dam. Also, we are only concerned with the RANGE of temperatures and not the temperature itself.

D. This could provide an alternate explanation as to why the fish are not reproducing. Therefore, this answer choice would actually weaken the argument.

E. What does this even tell us? This answer choice is irrelevant.
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Re: Emerald River Dam [#permalink] New post 25 May 2014, 16:36
ezinis wrote:
I WONDER IF THE TEMP. ACTUALLY DECREASES OR THE RANGE OF TEMP DOES. TRICKY QUESTION.


Second that. Is there a catch between range of temperature and actual increase/decrease in temperature?

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Re: Emerald River Dam [#permalink] New post 25 May 2014, 23:02
jlgdr wrote:
ezinis wrote:
I WONDER IF THE TEMP. ACTUALLY DECREASES OR THE RANGE OF TEMP DOES. TRICKY QUESTION.


Second that. Is there a catch between range of temperature and actual increase/decrease in temperature?

Cheers
J :)



There is no need to wonder over this one..even if the range decrease is true by the measured temps...it is something that the premise states explicitly..So it is just repeating an info that we already know..A dangerous trap in such questions

You might call it a trap though..coz the temperature drop decrease does not imply lower range..what if there was an increase in global temperatures altogether? :-D
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Re: Emerald River Dam   [#permalink] 25 May 2014, 23:02
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