We/ polluted/ air/ be/ smoke/ factories/ fumes/ motor vehicles//

A. What we have polluted the air with is smoke of factories and fumes of motor vehicles.

B. We are polluted the air which is smoke from factories and fumes from motor vehicles.

C. What we have polluted the air is smoke from factories and fumes from motor vehicles.

D. We polluted the air with smoke of factories and fumes of motor vehicles.