单项选择题

（）no gravity,there would be no air around the earth,hence no life.

A.If there was
B.If there had been
C.Were there
D.Had there been

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单项选择题
Making energy use completely harmless to the environment（）very difficult and usually economically expensive.

A.are
B.is
C.have been
D.shall be
单项选择题
The thief was so （）by teh bright lights and barking dogs that he left hastily.

A.frightened
B.annoyed
C.puzzled
D.disappointed
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