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
Human facial expressions differ from those of animals in the degree to which they can be deliberately controlled and modified.
A．sufficiently
B．noticeably
C．intentionally
D．absolutely
单项选择题
During the past ten years there have been dramatic changes in the international situation.
A．permanent
B．powerful
C．striking
D．practical
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