单项选择题

He has worked very hard ______ he entered the factory.

A．when
B．till
C．while
D．since
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单项选择题
We visited the room ______ they used as their lab last semester.
A．which
B．in that
C．where
D．in which
单项选择题
It's high time someone ______ Mike that each member of a team has to do his share of work.
A．could tell
B．tell
C．told
D．would tell
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