单项选择题

Doctors sometimes ______old cures when modem medicine doesn't work.

A．fall on
B．fall down on
C．fall back on
D．fall in upon
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单项选择题
Force is measured in pound ______it is produced.
A．whenever
B．how
C．no matter how
D．although
单项选择题
The men on board the ship pulled in the driver ______they feared was seriously injured.
A．whom
B．for whom
C．to whom
D．who
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