单项选择题

Only when he had done it ______ that he had made a mistake.

A．he then realized
B．did he realize
C．before he realized
D．he realized
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单项选择题
Many of the human problems associated with living in the ocean are ______ the problems of living in outer space.
A．just as
B．such as
C．such that
D．the same as
单项选择题
It has been proved that cockroaches (蝉螂) ______ for several weeks even after their heads have been cut off.
A．are surviving
B．can survive
C．surviving
D．that survive
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