单项选择题

Research discovered that plants infected with a virus give off a gas that______ disease resistance in neighboring plants.

A．contracts
B．activates
C．maintains
D．prescribes
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单项选择题
Because of the currency appreciation of RMB, many people ______dollar against RMB.
A．ran over
B．ran on
C．ran through
D．ran off
单项选择题
Even if its economy continues to recover, the US is increasingly becoming a nation of p. timers and temporary workers. This ______work force is the most important trend in American business today.
A．durable
B．disposable
C．available
D．transferable
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