We_______onitforseveralhoursbutwehavenot
问题:
We _______ on it for several hours but we have not yet reached any conclusion.
A.work
B.areworking
C.havebeenworking
D.havebeenworked
We _______ on it for several hours but we have not yet reached any conclusion.
A.work
B.areworking
C.havebeenworking
D.havebeenworked