When I try to find _______ that prevents so many people from taking part in the program,it seems to me that there are two main causes.?

A. why it does B. what it does?

C. what it is D. why it is?

When I try to find _______ that prevents so many people from taking part in the program,it seems to me that there are two main causes.

1. A.
   why it does
2. B.
   what it does
3. C.
   what it is
4. D.
   why it is