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  3. Early naturalists believed two species of beaver lived in North America: dam

Early naturalists believed two species of beaver lived in North America: dam

游客2025-02-19  18
问题     Early naturalists believed two species of beaver lived in North America: dam beavers and bank beavers. The bank species was thought to resemble the muskrat in behavior, living in burrows or lodges and unable to build dams. In fact, dams are primarily a strategy for dealing with annual variations in water levels. If water levels fall in summer, as they do in most of North America, then beavers lodge entrances may be exposed. With stabilized water levels, their homes are much safer. Along deep rivers, where bank beavers are found, this problem seldom arises. But these beavers do know how to build dams, and do so if the need arises, as may occur if they are forced to relocate after felling and consuming all nearby trees. [br] The passage implies which of the following about beavers?
选项 A、Bank beavers are unable to successfully compete with dam beavers when resources become scarce.
B、Differences in dam-building behavior among beavers do not necessarily imply multiple beaver species.
C、Building dams eventually causes beavers to deplete nearby resources.
D、When conditions permit, beavers are more likely to build dams than burrows or lodges.
E、In beavers, dam-building is an acquired rather than an innate skill.
答案 B
解析 本文的最终目的在于反驳第一句的早期观点。结合文中的论证可知，其实不存在岸边海狸和筑堤海狸的区别。A项文中没提竞争。C项文中也没提资源耗竭和建造水坝之间的区别。D项根据最后一句，当需求存在的时候，海狸会建造水坝，但是看不出来“更有可能”建造水坝。E项文中看不出建造水坝是后天习得还是天生的。
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