--- Listen! David is talking happily with his mother in the next room.--- It ______ be his mother. She has gone to Yunnan to be a volunteer doctor.
His father ________ in the factory since he was twenty.
--Be quiet! The children ____________ now. --Oh, sorry.
My brother __________ to Canada to learn English in 2005.
Jim, hurry up, ________ we’ll be late for the concert.
Look! The students are playing on the playground. Some are running, some are playing basketball, ________ are watching.