Critical Reasoning

In the late 1980's, the population of sea otters in the North Pacific Ocean began to decline. Of the two plausible explanations for the decline-increased predation by killer whales or disease-disease is the more likely. After all, a concurrent sharp decline in the populations of seals and sea lions was almost certainly caused by a pollution-related disease, which could have spread to sea otters, whereas the population of killer whales did not change noticeably.

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 substantial numbers of sea otters migrated to other locations from the North Pacific in the 1980's.
C. Along the Pacific coast of North America in the 1980's, 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.

OA: A

gmat_perfect wrote:In the late 1980's, the population of sea otters in the North Pacific Ocean began to decline. Of the two plausible explanations for the decline-increased predation by killer whales or disease-disease is the more likely. After all, a concurrent sharp decline in the populations of seals and sea lions was almost certainly caused by a pollution-related disease, which could have spread to sea otters, whereas the population of killer whales did not change noticeably.

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 substantial numbers of sea otters migrated to other locations from the North Pacific in the 1980's.
C. Along the Pacific coast of North America in the 1980's, 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.

Let's paraphrase the argument:

There are two possible causes for an event. Conclusion: cause #1 is more likely than cause #2.

When we're asked to weaken this form of argument, the correct answer will most likely make cause #2 more attractive.

So, our prediction: a reason why killer whales could be responsible for the decline in otters.

(A) fits the bill perfectly; even though killer whales don't usually snack on otters, the scarcity of the whales' normal food source has led whales to dine elsewhere.

Of importance, (A) doesn't require us to bring in any outside knowledge to support it; the stimulus itself provides the key fact: there's been a concurrent sharp decline in the populations of seals and sea lions, the whales' normal food source.

good explanation Stuart.

But E is also weakening the argument.

paes wrote:good explanation Stuart.

But E is also weakening the argument.

Feel, E is not relevant - it does not address either cause 1 or 2. Killer whale is not even mentioned

paes wrote:good explanation Stuart.

But E is also weakening the argument.

My 2 cents :

Pattern:

Event X is caused by A or B. The stem says A caused X.

How can we weaken it??? Just the opposite. A didnot cause X, whereas B caused X.

X: Decline in population of Seaotters

A: Pollution related disease

B: predation by Killer whales

From option A, we can directly weaken the premises on the stem is based.

paes wrote:good explanation Stuart.

But E is also weakening the argument.

bhai, can u plz just put across ur thought process. Let me see if i can construe something out of it...

may be option E is out of scope..but i am eager to see some explanation frm ur end..

So that we are not repeating the same mistake in the test...

Whats the source ?

Stuart Kovinsky wrote:

gmat_perfect wrote:In the late 1980's, the population of sea otters in the North Pacific Ocean began to decline. Of the two plausible explanations for the decline-increased predation by killer whales or disease-disease is the more likely. After all, a concurrent sharp decline in the populations of seals and sea lions was almost certainly caused by a pollution-related disease, which could have spread to sea otters, whereas the population of killer whales did not change noticeably.

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 substantial numbers of sea otters migrated to other locations from the North Pacific in the 1980's.
C. Along the Pacific coast of North America in the 1980's, 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.

Let's paraphrase the argument:

There are two possible causes for an event. Conclusion: cause #1 is more likely than cause #2.

When we're asked to weaken this form of argument, the correct answer will most likely make cause #2 more attractive.

So, our prediction: a reason why killer whales could be responsible for the decline in otters.

(A) fits the bill perfectly; even though killer whales don't usually snack on otters, the scarcity of the whales' normal food source has led whales to dine elsewhere.

Of importance, (A) doesn't require us to bring in any outside knowledge to support it; the stimulus itself provides the key fact: there's been a concurrent sharp decline in the populations of seals and sea lions, the whales' normal food source.

Thanks Stuart!
May I know what's wrong with C but?

In the late 1980's, the population of sea otters in the North Pacific Ocean began to decline. Of the two plausible explanations for the decline-increased predation by killer whales or disease-disease is the more likely. After all, a concurrent sharp decline in the populations of seals and sea lions was almost certainly caused by a pollution-related disease, which could have spread to sea otters, whereas the population of killer whales did not change noticeably.

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 substantial numbers of sea otters migrated to other locations from the North Pacific in the 1980's. - Strengthen
C. Along the Pacific coast of North America in the 1980's, sea otters were absent from many locations where they had been relatively common in former times. - Not related
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.- Outside of scope
E. The North Pacific populations of seals and sea lions cover a wider geographic area than does the population of sea otters. Not related

My Pick A

What is the Difficulty level for this Question?

Tricky one! I have never encountered such question with two causes. I spend a lot of time just
to understand what I was suppose to weaken.

(A)..Supports the Killer Whale reason

I think this was easy and direct.

A !

In my opinion A and E both have the scope to challenge the conclusion:

For A : This option is intact Up to point that whales rely on other preys(Probably sea otters) ,But how can we assume that the other prey are Sea otters .It could be possible that whales survive on star fish leaving the sea otter community unharmed. So still the scope is open for sea otters dying of pollution and not because they felt prey to whales

For E : the sea lions and seals are spread across larger geo area,If a certain area is affected by disease where the sea otters are not present and sea lions and seals were present then reduction in their total population(due to a certain pollution affected area) will say that seals died of pollution but sea otters did not die of pollution disease as they were not present in affected geo area . In this case E weakens the argument . but if the pollution disease was there where bot seals and otters were present then E can not be the answer.