单项选择题

There is a delicate balance of nature ______ many square miles of ocean and vegetation and clean air are needed to maintain only a relatively few human beings.

A. where
B. in which
C. when
D. how
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In 1914, an apparently insignificant event in a remote part of Eastern Europe ______ Europe into a great war.
A. inserted
B. plunged
C. pitched
D. imposed
单项选择题
He is ______ learned man, but she is ______ learned of all.
A. the most.., a most
B. the most.., the most
C. a most.., a most
D. a most.., the most
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