—I think the man over there must be Bob. -- It _______ be him. He has ______ to Australia.
---- __________________? -----For two hours.
_________ does Jim surf the Internet? Once a week.
_______he is busy, ________he helps us often.
Your child is only five. Is _____necessary for you to be so strict with him?
My mother always has__________ housework to do on weekends.