I think there are too many cars. If there .... (not/be) so many cars, there .... (not/be) so much pollution

 If I  (know) his number, I would phone him. 

Make questions with who or what:

 Something fell on the floor. 

We did well in the exam. We were relieved about that.

→ We were 

1. I have two sisters  ________________are doctors.

    A. both  of which                B. who both                C. both of whom                     D. whom both