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Passage 68
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.
文章解析
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.
從歷史情況來看，來自歐亞大陸的、能夠適應寒冷氣候的羚羊物種遷徙到氣候更加溫暖的非洲，和來自非洲的、能夠適應溫暖氣候的非洲羚羊遷徙到歐亞大陸，這兩類羚羊相比，前者數(shù)量更多。
這句話描述了一個事實，即從歐亞大陸遷徙到非洲的羚羊比從非洲遷徙到歐亞大陸的羚羊數(shù)量要多。
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.
對這種情況進行合理的解釋需要考慮到這樣一個事實，那就是跨大洲的遷徙既需要兩個洲之間有陸地橋梁，又需要在陸地橋梁上、以及跨越橋梁的沿線都有適宜的棲息地存在。
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.
在氣候變冷的時期，比如各種各樣的冰河時期，陸地橋梁長時期都是長期開放的（因為海平面很低）；而且能夠適應寒冷氣候的物種也能用到這個陸地橋梁，因為比較冷的棲息地是可以延伸直到橫跨過橋梁。
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.
在氣候變冷的時候，地球上的棲息地也會更多地朝赤道附近移動，受這個的影響，大部分的遷徙動物也就會隨著往靠近赤道的非洲移動。
In contrast, when the Earth is warm, the land bridge is reduced or gone because sea level is relatively high then.
相反，當?shù)厍驕囟缺容^高的時候，海平面相對來說會比較高一些，所以陸地橋梁就縮小了，甚至是消失了。
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.
只有在全球氣溫開始變化和水位做出反應之間的這短暫的時間差里，適應溫暖氣候的物種才能從赤道地區(qū)遷徙到緯度更高的地區(qū)。
先有全球氣溫開始變化，然后才有海平面水位做出反應（升高/降低），所以兩種現(xiàn)象之間有時間差。只有在這段時間差里（也就是氣溫開始變了，但海平面還沒有變化），適應溫暖氣候的物種才能機會遷徙到更冷的地方。
原文第三到第六句詳細解釋了為什么往溫度比較高的地方遷徙的物種要多于往溫度比較低的地方遷徙的物種。總結來說，是因為相比于氣候溫暖的時候，大陸橋梁更容易在氣候寒冷的時候存在，而氣候寒冷的時候，動物們會從氣候寒冷的地方遷徙到氣候溫暖的地方。
題目解析
1. According to the passage, which of the following is true of an Eurasia-Africa land bridge during ice ages?
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.
第一題：根據(jù)文章內(nèi)容，以下哪個關于冰河時期的歐亞大陸和非洲之間的大陸橋梁的說法是正確的？
A. 它為適應寒冷氣候的羚羊物種提供了舒適的棲息地。（該選項是對原文第三句的同義改寫。）
B. 它鼓勵適應寒冷氣候的羚羊物種從非洲遷徙到歐亞大陸。
C. 它讓適應溫暖氣候的羚羊物種存活了下來，否則這些羚羊物種就可能會滅絕。
D. 它更可能存在于冰河世紀的早期，而不是冰河世紀的晚期。
E. 它提供的棲息地比其他時期的大陸橋梁所提供的棲息地變化得更快。
2. The author of the passage implies that during the “short lag”, a land bridge between Africa and Eurasia would
A. be inhabited primarily by species of antelope originating in Eurasia.
B. be characterized by areas of widely varying elevation above sea level.
C. be inhabited by a wide diversity of antelope species.
D. contain habitats that could sustain warm-adapt antelope species.
E. contain habitats similar to habitats at much higher latitudes in Eurasia.
第二題：作者認為，在短暫的時間差（short lag）里，連接非洲和歐亞大陸之間的大陸橋梁會怎么樣？
B. 那邊不同區(qū)域之間的高度相差很大（以海平面為標準）。
D. 那里有可以支持適應溫暖氣候的羚羊物種生存的棲息地。（該選項是對原文第六句的同義改寫。）
3. According to the passage, which of the following best accounts for the apparent bias in antelope-migration direction?
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.
第三題：根據(jù)文章內(nèi)容，以下哪個選項最能解釋羚羊物種的遷徙方向上的傾向？
A. 適應溫暖氣候的羚羊無法忍受寒冷的棲息地，而適應寒冷氣候的羚羊往往可以忍受比較炎熱的棲息地。
B. 在全球氣溫上升的時候，大陸橋梁沒有適合適應溫暖氣候的羚羊生存的棲息地。
C. 在大部分的氣候條件下，相比于歐亞大陸，非洲能為羚羊提供更多的適宜的棲息地。
D. 源自歐亞大陸的羚羊物種數(shù)量比源自非洲的羚羊物種數(shù)量多。
E. 相比起氣候變化有利于動物往溫度更低的地方遷徙的時候，氣候變化有利于動物往溫度更高的地方遷徙的時候，陸地橋梁更容易存在。（根據(jù)原文第三到第六句的內(nèi)容，陸地橋梁在氣候比較寒冷的時候更容易存在，而氣候變冷的時候，地球上的棲息地也會更多地朝赤道附近移動。而在氣候比較溫暖的時候，陸地橋梁會縮小，甚至是消失沒有了。）
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