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
Remember to ask for a______ of quality for the consumer goods; otherwise they will not of- fer any maintenance.
A．certificate
B．mark
C．warranty
D．receipt
单项选择题
In the face of the evidence, the criminal had to______ his guilt to the court.
A．admit
B．acknowledge
C．accept
D．confess
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