private cars are bringing us convenience they may also cause traffic accidents and pollut

问题补充：

private cars are bringing us convenience, they may also cause traffic accidents and pollution.

A. When

B. Since

C. while

D. As

答案：

A. When

B. Since

(答案→)C. while

D. As

解析：句意:尽管私人车辆给我们带来了方便，然而他们也可能引起了交通事故和污染。while虽然，尽管。所以选C。