单项选择题

The troops have been on the（）for a possible enemy attack.

A．alarm
B．alert
C．warning
D．notice

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单项选择题
If you hear the fire（）, leave the building quickly.

A．warning
B．alarm
C．signal
D．bell
单项选择题
He drove fast and arrived an hour（）schedule.

A．in advance
B．before
C．by
D．ahead of
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