Official Explanation

Argument Construction

This question asks us for an assumption required by the hypothesis.

The researchers noted that the flies that had been conditioned to associate a particular odor with an electric shock were much less likely to avoid the odor when they were tested individually than when they were tested as a part of a group.

Based on this fact, the researchers hypothesized that the flies that had retained the conditioning would give off an alarm when they detected the odor. This alarm would then retrigger the association among the other flies, leading them to avoid the odor.

We must consider whether there is some other fact that could explain why the flies were more likely to respond to the odor in a group than when they are alone. If there were, that alternative explanation would severely call into question the researchers' hypothesis. The hypothesis therefore requires that any such alternative explanation be false.

A. It is possible that the flies do in fact give off odors as an alarm signal. Because the nature of the flies' alarm signal is not specified by the hypothesis, this is entirely consistent with the hypothesis and would not undermine it. Therefore, the hypothesis does not require that flies do not give off odors as alarm signals.

B. Correct. Suppose that the flies that did not avoid the odor when tested individually were more likely to avoid the odor when in groups. This may be simply because these flies were following the movements of the flies that were triggered. That is, the signal did not cause the other flies' reactions. Instead, the movements of the triggered flies did. It follows that this possibility must be ruled out in order for the hypothesis to be plausible, and this answer choice does precisely that.

C. The hypothesis would actually be more plausible if this statement were false. That is, the hypothesis would be more plausible if the flies that did not avoid the odor when tested individually were just as likely, when they were tested in a group, to avoid the odor as the other flies in the group.

D. The hypothesis is perfectly compatible with the assumption that, prior to their conditioning, the flies were entirely indifferent to the odor.

E. The principle of association—that the shock is associated with the odor even when the shock itself is not present—actually requires that this statement be false.

The correct answer is B.