Since life began eons ago, thousands of creatures have come and gone. Some, such as the dinosaurs, became extinct due to natural

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问题     Since life began eons ago, thousands of creatures have come and gone. Some, such as the dinosaurs, became extinct due to naturally changing ecologic conditions. More recent threats to life forms are humans and their activities. Man has drained marshes, burned prairies, dammed and diverted rivers. Some of the more recent casualties of man’s expansion have been the dodo, great auk, passenger pigeon, Irish elk, and Steller’s sea cow. Sadly, we can no longer attribute the increasing decline in our wild animals and plant species to "natural" processes. Many species are dying out because of exploitation, habitat alteration or destruction, pollution, or the introduction of new species of plants and animals to an area. As mandated by Congress, protecting endangered species, and restoring them to the point where their existence is no longer jeopardized, is the primary objective of the U.S. Fish and Wildlife Service’s Endangered Species Program.
Which of the following is a form of man’s habitat alteration?

选项 A、Glacial encroachment.
B、Hurricanes.
C、Dammed rivers.
D、Snowstorms.

答案C

解析 见文中第三、四句:More recent threats to life forms are humans and their activities. Man has drained marshes,burned prairies,dammed and diverted rivers.各种生物近期遇到的威胁更多来自于人类:人类耗干了湿地、烧毁了大草原、筑坝并让河流改道。因此C.“人类生活环境变迁的一种形式是在河流上筑坝。”为答案,其余A.“冰川侵蚀”、B.“飓风”和D,“暴风雪”均是自然现象。
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