单项选择题

Air is composed of______ gas including hydrogen, oxygen and carbon dioxide.

A．varied
B．variant
C．variable
D．various
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单项选择题
Hardly a month goes by without______ of another survey revealing new depths of scientific illiteracy among US citizens.
A．words
B．word
C．a word
D．the word
单项选择题
You can't let the situation get worse. You must take ______.
A．decisions
B．sides
C．directions
D．steps
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