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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 is true of an Eurasia-Africa land bridge during ice ages?
选项 A、It offers suitable habitats for cold-adapted species of antelope.
B、It encourages migration from Africa to Eurasia of cold-adapted species of antelope.
C、It allows the survival of warm-adapted species of antelope that might otherwise home extinct.
D、It is more likely to exist early in an ice age than later in an ice age.
E、The habitats it offers change more quickly than do those offered by land bridges during other periods.
答案A
解析 根据文章，羚羊迁徙需要大陆桥以及大陆桥上有适宜的栖息地。B项表述相反，应该是从欧亚大陆迁徙到非洲。C项文章只提及寒冷时期耐寒的物种会往温暖的地方迁徙，没提及是否让适应温暖环境的物种生存。D项根据short lag的部分可知，当冰河时代快结束的时候，在海平面上升之前，大陆桥依然会存在，因此看不出冰河时代开始和结束的时候什么阶段的大陆桥多。E项文中没提栖息地的变化。
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