单项选择题

They repeated the experiment several times __________ they were sure that the result was reliable.

A．until
B．for
C．since
D．when
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单项选择题
The road __________ I drive to work is always crowded.
A．which
B．on that
C．that
D．on which
单项选择题
He was praised for __________ such a contribution to the country.
A．make
B．to make
C．to making
D．having made
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