单项选择题

We must______that the experiment is controlled as rigidly as possible.

A．assure
B．secure
C．ensure
D．issue
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单项选择题
You______John in the street this morning. He’ s been dead for ages.
A．mustn’t see
B．mustn’ t have seen
C．couldn’t see
D．couldn’ t have seen
单项选择题
I need to move to a larger apartment. Do you know of any ______ one in this neighborhood
A．vacant
B．bare
C．blank
D．empty
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