—Has Sam finished his homework?
—I have no idea. He _____ it this morning.
A.did
B.has done
C.was doing
D.had done
—Has Sam finished his homework?
—I have no idea. He _____ it this morning.
A.did
B.has done
C.was doing
D.had done
C
根据句意，答语意为不知萨姆是否已做完，由时间状语this morning可推知，他一整上午都在做，即过去一段时间内一直在进行的动作。