单项选择题

The human beings have polluted the environment seriously. It is time the United Nations must take some measures.

A. take
B. taking
C. to take
D. took
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单项选择题
Any troop of wild animals should be approached warily.()

A. fearlessly
B. confidently
C. silently
D. prudently
单项选择题
The people of China are working very hard to make concerted efforts to invigorate the country.
A．enjoyable
B．persistent
C．encouraged
D．joint
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