单项选择题

Researchers discovered that plants infected with a virus give off a gas that （） disease resistance in neighboring plants.

A．contracts
B．maintains
C．prescribes
D．activates

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单项选择题

Crimes of violence appear to be quite （）, but psychologists can usually find a motive hidden away in the criminal's childhood.

A．senseless
B．sensational
C．nonsensical
D．sensitive

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