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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.
题目： vole一般群居，两三窝住一起。但是发现深秋到冬天，一窝里边的vole数目，要比春天到初夏的一窝里边的vole数目多。问哪个选项能解释这种季节性的变化跟幼崽的死亡率的季节性变化相关。
关键字：幼崽的死亡率的季节性变化。
也就是说选项要跟幼崽死亡有关。
A 高比例，跟比例无关，讲的是数量。
B 年年不一样，无关
C 主要靠吃叶子，那就部分成年还是幼崽了，不能解释
D 冬天生存环境严酷，那应该冬天的数目更少，不能解释
E 春天到初秋有蛇吃幼崽，对的
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