Critical Reasoning

In the late 1980s, the population of sea otters in the North Pacific began to decline. There are two plausible explanations for the decline: predation, possibly by killer whales, or disease. Of these two, disease is the more likely, since a concurrent sharp decline in populations of seals and sea lions is believed to have been caused by disease, and diseases that infect these creatures are likely to be able to infect sea otters also.

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

(A) Killer whales in the North Pacific usually prey on seals and sea lions but will, when this food source is scarce, seek out other prey.
(B) There is no indication that the sea otter population at any North Pacific location declined in the 1980s because of substantial numbers of sea otters migrating to other locations.
(C) Along the Pacific coast of North America in the 1980s, sea otters were absent from many locations where they had been relatively common in former times.
(D) Following the decline in the population of the sea otters, there was an increase in the population of sea urchins, which are sea otters' main food source.
(E) The North Pacific populations of seals and sea lions cover a wider geographic area than does the population of sea otters.

I was between A and B. Which one is correct?

Why the other one is wrong?

Thanks.

gmat_perfect wrote:In the late 1980s, the population of sea otters in the North Pacific began to decline. There are two plausible explanations for the decline: predation, possibly by killer whales, or disease. Of these two, disease is the more likely, since a concurrent sharp decline in populations of seals and sea lions is believed to have been caused by disease, and diseases that infect these creatures are likely to be able to infect sea otters also.

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

(A) Killer whales in the North Pacific usually prey on seals and sea lions but will, when this food source is scarce, seek out other prey.
(B) There is no indication that the sea otter population at any North Pacific location declined in the 1980s because of substantial numbers of sea otters migrating to other locations.

I was between A and B. Which one is correct?

Why the other one is wrong?

Thanks.

IMO A is better than B. I somehow find B irrelevant because it brings migration into the picture. B says there was no indication of decline in population BUT does not talk specifically about decline as a result of killer whales or disease. So we cant really infer that its weakening the conclusion directly. Also, it brings migration into the picture, which I find irrelevant.

A on the other hand does talk about the possibility of killer whales driving the decline in sea otters.

Whats the OA?

I believe A is the answer.

B is actually strengthening our point that if migration is not the cause then it increases the chances of disease and predation to be the cause are more likely.

Rest are not not related and E is also strengthening our point.

So A is the answer.

Gmatperfect,

I remembered this question.U posted the same question before and explained by stuart.Check this.

https://www.beatthegmat.com/sea-otters-t59820.html

gmat_perfect wrote:In the late 1980s, the population of sea otters in the North Pacific began to decline. There are two plausible explanations for the decline: predation, possibly by killer whales, or disease. Of these two, disease is the more likely, since a concurrent sharp decline in populations of seals and sea lions is believed to have been caused by disease, and diseases that infect these creatures are likely to be able to infect sea otters also.

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

(A) Killer whales in the North Pacific usually prey on seals and sea lions but will, when this food source is scarce, seek out other prey.
(B) There is no indication that the sea otter population at any North Pacific location declined in the 1980s because of substantial numbers of sea otters migrating to other locations.
(C) Along the Pacific coast of North America in the 1980s, sea otters were absent from many locations where they had been relatively common in former times.
(D) Following the decline in the population of the sea otters, there was an increase in the population of sea urchins, which are sea otters' main food source.
(E) The North Pacific populations of seals and sea lions cover a wider geographic area than does the population of sea otters.

I was between A and B. Which one is correct?

Why the other one is wrong?

Thanks.

Though the ans is A. The real confusion was b/w A and E.
Actually B is not weakening but strengthening the conclusion

The conclusion is based on the comparison of Seals and Sea Lions AND Otter. It is assumed that they are comparatively similar in most of the aspects.

E says that they are different in one aspect.

Experts pls help in this.

He doesn't like to search his own questions on the internet. I am not sure whether he knows how to search

selango wrote:Gmatperfect,

I remembered this question.U posted the same question before and explained by stuart.Check this.

https://www.beatthegmat.com/sea-otters-t59820.html

We're looking to weaken the reasoning. The author concludes that disease is more likely to cause the decline of sea otters because seals and sea lions have been caused by disease.

(A) offers support for the alternate explanation for the decline of sea otters (predation) WITHOUT contradicting the information given about the decline of seals and sea lions.

(E) is irrelevant and out of scope. It doesn't weaken the disease argument and it doesn't strengthen the predation argument.

This is tricky. I am not choosing A because passage says 'concurrent' sharp decline. If A is true, otters will decline after the seals and lions and their decline won't be concurrent. If the premise didn't have this work, A would fit in great.

Anybody thinks it might be E? If seals and lions are not localized to N. Pacific, their disease makes the otters in N. Pacific less likely to be diseased too. Same question was posted in a previous thread (link above) but expert has not explained why not E.