问题

We must do something to _ the factories sending outpoisonous gases so as to keep the city_.[ ]

A: keep; being polluted
B: keep; from being polluted
C: prevent; being polluted
D: prevent; from being polluted

正确答案是：

同类题型

__________ the small boy __________ a round face like

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Greatly ________, the students made up their minds to carry ________ the experiment.[ ]

What does your father do-______________.

“Mike is often absent from class.” “Tell him he _________ answer for it if he goes on behaving like that.”