Question

Something must be done to prevent factories sending out poisonous gases so as to keep the city _________.
A polluting          B. from polluting    C. pollute          D. from being polluted

Answer 1

D

考查动词搭配。keep … from doing sth.阻止某人做某事，根据句意是阻止城市被污染，故用被动，选D。