单项选择题

It is recommended that the screw ______ to increase accuracy of measurement.

A．is used
B．was used
C．be used
D．had been used
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单项选择题
He didn't pass the exam ______ that he hadn't studied hard.
A．on
B．×
C．in
D．up to
单项选择题
______ did the refugees receive help from countrymen.
A．At a time
B．At all time
C．At no time
D．At anytime
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