单项选择题

Parachutes are not a new invention.

A．a valuable
B．a lucky
C．a recent
D．an unknown
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It is not so convenient to use only______
单项选择题
One of the responsibilities of the Coast Guard is to make sure that all ships obediently follow traffic rules in busy harbors.
A．skillfully
B．safely
C．dutifully
D．currently
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