单项选择题

In our class, when the bell rang and the teacher closed his book, it was a () for everyone to stand up.

A．signal
B．chance
C．mark
D．measure

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单项选择题
The computer revolution may well change society as () as did the Industrial Revolution.

A．certainly
B．insignificantly
C．fundamentally
D．comparatively
单项选择题
The machines are made ()at full speed.

A．work
B．working
C．to work
D．to be worked
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