单项选择题

Hydrocarbons, ______ by engine exhausts, react with nitrogen oxides in the presence of sunlight to form complex toxic gases.

A．are given off
B．give off
C．they are given off
D．given off
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单项选择题
The doctor's ______ is that she'll soon be as good as new if she takes insulin and watches her diet.
A．agnosticism
B．anticipation
C．diagnosis
D．prognosis
单项选择题
Leaving for work in plenty of time to catch the train will ______ worry about being late.
A．rule off
B．prevent
C．avoid
D．obviate
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