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问题 选择题

下列变化是由于加成反应造成的是

A．CH4与Cl2的混合气体光照后颜色变浅

B．苯加入溴水中用力振荡，静止后水层变为无色

C．C2H4通入酸性KMnO4溶液中，溶液紫色逐渐变浅

D．C2H4通入Br2的CCl4溶液中，溶液褪色

答案

答案：D

A．取代反应； B．物理变化，萃取； C．不正确，是氧化反应； D．加成反应。选D。

单项选择题

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 has become extinct due to man’s destruction

A．African elephant.

B．Irish elk.

C．Giant panda.

D．White Bengal.
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单项选择题

在上网发行资金申购流程中，发行人和主承销商应在（）日前提供确定的发行价格。

A．T+1

B．T+2

C．T+3

D．T+4
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