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题库 / Prep2007E1-CR-3
The prairie vole, a small North American grassland rodent, breeds year-round, and a group of voles living together consists primarily of an extended family, often including two or more litters. Voles commonly live in large groups from late autumn through winter; from spring through early autumn, however, most voles live in far smaller groups. The seasonal variation in group size can probably be explained by a seasonal variation in mortality among young voles.
Which of the following, if true, provides the strongest support for the explanation offered?
It is in the spring and early summer that prairie vole communities generally contain the highest proportion of young voles.
Prairie vole populations vary dramatically in size from year to year.
The prairie vole subsists primarily on broad-leaved plants that are abundant only in spring.
Winters in the prairie voles' habitat are often harsh, with temperatures that drop well below freezing.
Snakes, a major predator of young prairie voles, are active only from spring through early autumn.
果因。答案一定要提及年轻幼崽 和 死亡率
D． 冬天时vole的生存环境恶劣（那么冬天应该人口少，不应该是大团队，和原文段的前提矛盾）
E． 蛇是年轻vole的主要捕食者，主要在春天和早秋活跃（捕食者活跃高，那么vole死亡率高，合理地解释了这段时间死亡率高的原因）
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