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

A.to be polluted

B.from polluting

C.from being polluted

D.polluting

646._______ the obvious differences in size and population,the states of America have many things ________ common.

A.Although;on

B.Though;in

C.In spite of;in

D.Because of;on

645.答案是C;

prevent our city from being polluted 阻止城市受污染。

646.答案是C;

have sth.in common with sb.与某人有共同之处。