单项选择题

The doctor will not perform the operation ______ it is absolutely necessary.

A．so
B．if
C．for
D．unless
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______ is well known, the key to success lies in hard work.
A．As
B．That
C．Which
D．What
单项选择题
The teacher, as well as all his students, ______ by the dancer's performance.
A．was impressed
B．had impressed
C．impressed
D．were impressed
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