1. Seeing everything________, the professor left the lab happily.
A.done B.did C.do D.doing
2.The meeting ______ tomorrow will be of great importance. All of us should attend it.
A . held B.to be held C.being held D.is going to be held
3.The old man,_______ abroad for 20 years, is on the way back to his mother land.
A.to work B.working C.to have worked D.having worked
