________ Reyes admits that he has enjoyed a quick rise to the top, the road to success has not always been smooth.

1. A.
   While
2. B.
   Since
3. C.
   As
4. D.
   If

         Reyes admits that he has enjoyed a quick rise to the top, the road to success has not always been smooth.

A．While              B．Since        C．As            D．If