It is _______ he often fails in exam_______ makes his parents worried about him.

A. because, that      B. that, that        C. 不填,  that     D. what, that

It is_______ he often fails in exam_______ makes his parents worried about him.

1. A.
   because, that
2. B.
   that, that
3. C.
   不填, that
4. D.
   what, that

It is_______ he often fails in exam_______ makes his parents worried about him.