5

Set 2: Command of Evidence

Explanation

Answer: A

PASSAGE

Biologists studying blue whales in the Pacific Ocean noticed that their calls have been deepening in pitch over the last few decades. One hypothesis is that as the population recovers from whaling, whales must call deeper to be heard over the noise of other whales.

Which finding, if true, would most weaken this hypothesis?

A. Blue whale populations have increased significantly since the ban on whaling.✓ Correct
B. Ocean noise from ships has also increased during the same period.
C. Whales in populations that have NOT recovered are also calling deeper.
D. Deeper calls travel further underwater than higher-pitched calls.

Detailed Explanation

The hypothesis links deeper calls to *population recovery* (competition for sound space). If whales in *unrecovered* populations (low density) are also calling deeper, then population density cannot be the cause, weakening the hypothesis.

Why others are wrong: A (This would establish the premise (population increase) is true, which doesn't weaken the link.), B (Increased ship noise might offer an *alternative* explanation, but C is a more direct rebuttal of the specific population mechanism.), D (This explains *why* they might call deeper (physics), not *what cause* triggered the change.).

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