Every fall Croton's jays migrate south. The jays always join flocks of migrating crookbeaks with which they share the same summer and winter territories. If a jay becomes separated from the crookbeaks it is accompanying, it wanders until it comes across another flock of crookbeaks. Clearly, therefore, Croton's jays lack the navigational ability to find their way south on their own. Which of the following, if true, most strengthens the argument above? A. Croton's jays lay their eggs in the nests of crookbeaks, which breed upon completing their southern migration. B. The three species most closely related to crookbeaks do not migrate at all. C. In the spring, Croton's jays migrate north in the company of Tattersall warblers. D. Species other than Croton's jays occasionally accompany flocks of migrating crookbeaks. E. In the spring, crookbeaks migrate north before Croton's jays do.
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发表于 2012-8-13 23:40:44
