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
Here __________ a pen, a few envelopes and some paper for you.
A．is
B．are
C．be
D．being
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