单项选择题

Try the experiment yourself ______you will know the reason.

A．so
B．and
C．or
D．unless
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单项选择题
The streets are all day. It______ during the night.
A．can't have rained
B．mustn't have rained
C．couldn't rain
D．shouldn't have rained
单项选择题
______is a fact that English is being accepted as an international language.
A．This
B．There
C．That
D．It
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