The children ______ a P.E. class on the playground when it began to rain suddenly.

May I speak to Mr Wang?—Sorry. He______ a speech now. Please call later.

do you go to visit your grandpa?—Once or twice in a week.[ ]

How long ____ to finish the work?

Someone is knocking at the door. Who may it be? —It ______ be Tom. He is still in the school.