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.