LSAT Feb 1993 Weaken

[nonameee]

22. A scientist made three observations: (1) in the world's temperate zones, food is more plentiful in the ocean than it is in fresh water; (2) migratory fish in temperate zones generally mature in the ocean and spawn in fresh water; and (3) migratory fish need much nourishment as they mature but little or none during the part of their lives when they spawn. On the basis of those observations, the scientist formulated the hypothesis that food availability is a determining factor in the migration of migratory fish. Subsequently the scientist learned that in the tropics migratory fish generally mature in fresh water and spawn in the ocean.

Which one of the following would it be most helpful to know in order to judge whether what the scientist subsequently learned calls into question the hypothesis?

(A) whether in the world's temperate zones, the temperatures of bodies of fresh water tend to be lower than those of the regions of the oceans into which they flow

(B) whether the types of foods that migratory fish eat while they inhabit the ocean are similar to those that they eat while they inhabit bodies of fresh water

(C) whether any species of fish with populations in temperate zones also have populations that live in the tropics

(D) whether there are more species of migratory fish in the tropics than there are in temperate zones

(E) whether in the tropics food is less plentiful in the ocean than in fresh water





I got the question right. But I'm not sure why B is wrong here. My reasoning with B goes like this:

If the fish in tropical area moved into the ocean or fresh water not in accordance with food availability in them (which is the author's hypothesis), then it would show another reason for the behavior of the fish. Thus, it would weaken his argument.

Please explain.

OA: E

[nonameee]

I think I got it:

First of all, what will the correct answer accomplish?
Quote:
Which one of the following would it be most helpful to know in order to judge whether what the scientist subsequently learned calls into question the hypothesis?

In other words, the correct answer would provide the info on why the second observation questions the scientist's hypothesis; i.e., the second observation will weaken his hypothesis in light of the new information provided by the correct answer.
Quote:
(B) whether the types of foods that migratory fish eat while they inhabit the ocean are similar to those that they eat while they inhabit bodies of fresh water

If we answer 'yes' to this question, will the second observation weaken the hypothesis?

No. If the food is similar everywhere, then it doesn't refute the hypothesis that fish travel in accordance with the availability of food.

If we answer 'no' to this question, will the second observation weaken the hypothesis?

No. Imagine that in the ocean fish eat mollusks type A, and in fresh water they eat mollusks type B. If for the growing phase of their life they need mollusks type A, and these mollusks are available in the ocean in temperate zones and in fresh water in tropics. Fish behavior in tropics is again explained by the hypothesis, and the hypothesis is not refuted by this info.

Therefore, knowing the information from (B), will not help the second observation to refute the hypothesis.