_______can be done has been done.

A. Which　 B. When　 C. What　 D. That

All ___ can be done has been done.

A. what    B. that    C. which      D. the one

 All __________ can be done has been done.

A. which             B. that               C. /               D. what

Everything ________ can be done has been done.

[　　]

All __________ can be done has been done

1. A.
   which
2. B.
   that
3. C.
   /
4. D.
   what