—Who______ it be that is knocking at the door? —It ______ be Father, but I’m not sure.
Scientists say it may be five or six years _____ it is possible to test this medicine to human patients.
At last we reached a lonely village, _______ a beautiful river.
It was the training ______ he had as a young man _____ made him such an excellent speaker.
---Why did you leave that position?---I a better position at IBM.
--Have you got the leaving time of the train for me?---Yes, but you’d better ____of it by yourself.