Something must be done to prevent our city by thick smoke.A. to be polluted B. from poll

问题补充：

Something must be done to prevent our city by thick smoke.

A. to be polluted

B. from polluting

C. from being polluted

D. polluting

答案：

A. to be polluted

B. from polluting

(答案→)C. from being polluted

D. polluting

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