问题
选择题
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
答案
答案：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。