Explanation
The argument assumes that the crows' ability to recognize and react to the masks is not limited to the individual crows that were initially trapped. It implies that this recognition can be communicated to crows that were not directly involved in the initial incident.
A. (Correct Response) The argument assumes that the crows that reacted aggressively were not necessarily the ones that had been trapped. This is a crucial assumption because if only the trapped crows had reacted, it would not support the conclusion that crows can pass on information about specific threats to other crows.
B. The study does not rely on the assumption that crows always react to perceived threats in the same manner. It's the specific reaction to the masks that is noted, not a generalized behavior pattern.
C. The argument is about crows, specifically, and does not make any claims about the behavior of other bird species, nor does it depend on such a comparison.
D. The argument is based on a specific set of observations involving crows that had been exposed to the masks during trapping. There is no mention of crow behavior in places where no crows have been captured, so the argument does not depend on this assumption.
E. The argument does not hinge on the crows' ability to distinguish human faces but rather their ability to recognize and respond to the masks, which are associated with a threatening experience.
The assumption that some of the crows reacting to the masks were not the same individuals that had been trapped is necessary for the conclusion that crows can communicate threats to each other, which supports the correct answer, option A.