________ for more than three months, but he did his best to catch up with his classmates．

1. A.
   Being ill
2. B.
   Having been ill
3. C.
   Though he was ill
4. D.
   He was ill

_____ for more than three months, but he did his best to catch up with his classmates.

A. Being ill  B. Having been ill  C. Though he was ill  D. He was ill