He would have attended your birthday party but he ________ himself with a very important experiment．

1. A.
   occupied
2. B.
   has occupied
3. C.
   had occupied
4. D.
   has been occupying

He would have attended your birthday party but he ______ himself with a very important experiment.

   A. occupied      B. has occupied        C. had occupied      D. has been occupying

He would have attended your birthday party but he _________ himself with a very important experiment.

A．occupied   B．has occupied    C．had occupied    D．has been occupying