单项选择题

The most crucial problem any economic system faces is how to use its scarce resources.

A．puzzling
B．difficult
C．terrifying
D．urgent
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单项选择题
Smoking is inhibited in public places.
A．instructed
B．inquired
C．forbidden
D．strived
单项选择题
How can we reduce the risk of cancer
A．cut in
B．cut down
C．cut off
D．cut out
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