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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.
A． 春天和早夏有更多的年轻vole（没有提到死亡率和团队的大小关系）
B． Vole的人口每年都不一样（不看前提，该选项可以加强，但无法证明前提和结论的推理关系）
C． Vole主要吃一种在春天才有的植物（那么春天应该人口多，不应该是小团队，和原文段的前提矛盾）
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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