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
<上一题 目录 下一题>
热门 试题

单项选择题
He could hardly ______ his temper when he saw the state of his office.
A．hold in
B．hold up
C．hold off
D．hold out
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
相关试题