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  3. In mountainous regions, the timberline is the highest altitude at which trees grow. In the Rocky Mountains, the current timberli

In mountainous regions, the timberline is the highest altitude at which trees grow. In the Rocky Mountains, the current timberli

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问题     In mountainous regions, the timberline is the highest altitude at which trees grow. In the Rocky Mountains, the current timberline is at the altitude above which growing season temperatures remain cooler than 10 degrees centigrade. Fossilized remains of trees that grew 10,000 years ago have been found 100 meters above the current Rocky Mountain timberline. Clearly, therefore, the climate of the Rocky Mountains is cooler now than it was 10,000 years ago.
    Which of the following is an assumption on which the argument relies?
选项 A、In the past 10,000 years, the only trees to have grown above today’s timberline are the trees whose fossilized remains been found.
B、No trees grew 10,000 years ago at altitudes higher than the ones at which fossilized tree remains have been found.
C、The fossils are not of species of trees that were able to tolerate cooler growing temperatures than are the species that currently grow near the timberline.
D、The Rocky Mountains have not eroded significantly over the past 10,000 years.
E、The climate of the Rocky Mountains has never been significantly warmer than during the lifetime of the trees whose fossilized remains have been found.
答案C
解析 化石所属的物种的耐低温能力比目前生长在林木线附近的物种强→不是因为过去温度高导致林木线以上存在树木，而是因为以前的树木耐低温能力强→削弱原文结论，C正确。A项选项取反。唯一生长在今天林木线以上的树不是发现了化石残骸的树→还有其他树生长在林木线以上→进一步加强过去温度比现在高，没有削弱原文，不选。B项选项取反。1万年之前，有树生长在发现了化石残骸的高度以上→加强过去的温度比现在的温度高，没有削弱原文，不选。D项山脉的侵蚀和林木线的高度无关，不选。E项重复原文结论，不选。
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