问题
单项选择题
牙骨质中含有机物和水的重量比为( )
A．约40%～50%
B．约50%～55%
C．约60%～70%
D．约70%～80%
E．约80%～90%
答案
参考答案：B
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牙骨质中含有机物和水的重量比为( )
A．约40%～50%
B．约50%～55%
C．约60%～70%
D．约70%～80%
E．约80%～90%
参考答案：B
| 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 Wilidlife Service’s Endangered Species Program. |
The tone of this passage is
A．nationalistic.
B．pro-wildlife.
C．anti-wildlife.
D．feminist.
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