We must do what we can to the river .A. protect; against pollutingB. stop; pollutingC. kee

问题补充：

We must do what we can to the river .

A. protect; against polluting

B. stop; polluting

C. keep; being polluted

D. prevent; from being polluted

答案：

A. protect; against polluting

B. stop; polluting

C. keep; being polluted

(答案→)D. prevent; from being polluted

解析：考查固定词组。固定词组：prevent sb from doing sth阻止某人做某事；句意：我必须坐我们能做地阻止河流被污染。根据句意说明存在着被动的关系，故使用动名词的被动语态。故D正确。