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  3. Historically, more cold-adapted antelope species originating in Eurasia have migrated into Africa, where the climate is generall

Historically, more cold-adapted antelope species originating in Eurasia have migrated into Africa, where the climate is generall

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问题     Historically, more cold-adapted antelope species originating in Eurasia have migrated into Africa, where the climate is generally warmer, than have warm-adapted African species into Eurasia. A likely explanation for this involves the fact that intercontinental migrations require both a land bridge connecting the two continents and the suitable habitat both on and across that land bridge. During periods of climatic cooling, such as the various ice ages, the land bridge is open for a long time (because sea level remains low) and is usable by cold-adapt species because cool habitats then extend across it. Thus during cooling most migrants would be expected to travel toward Africa, which is near the equator, since this is the direction dictated by habitat changes on a cooling Earth. In contrast, when the Earth is warm, the land bridge is reduced or gone because sea level is relatively high then. Only during the short lag between onset of global temperature change and sea level response can warm-adapted species migrate from the equator toward higher latitudes.
According to the passage, which of the following best accounts for the apparent bias in antelope-migration direction?
选项 A、Warm-adapted antelope species are rarely able to tolerate cool habitats, whereas cold-adapted antelope species usually can tolerate warm habitats.
B、During global warming periods, land bridges, when present, lack habitats suitable for sustaining warm-adapted antelope species.
C、Under most climatic conditions, Africa offers a larger number of suitable antelope habitats than does Eurasia.
D、Many more species of antelope have originated in Eurasia than have originated in Africa.
E、Land bridges are more likely to exist when climate change favors migration to warmer climates than when climate changes favors migration to cooler climates.
答案E
解析 “气候变化适合迁徙到温暖环境中时”指的就是全球变暖的时候，根据文章，这个时候大陆桥更可能存在。但是气候变暖时，大陆桥只会存在很短的一段时间，所以选项E正确。A项文章本身没讨论羚羊对于温度的适应性问题，而且决定羚羊往哪个方向迁徙的因素是大陆桥和大陆桥上的栖息地，而非动物的忍耐性。B项当全球变暖时，在short lag期间，大陆桥上依然有合适的栖息地。C项从文中看不出来。D项从文中看不出来。
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