--- 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.
----How about having a picnic next weekend? ---- It _____great.
Lucy is ill.She has a bad cold for several days.
Yougo and ask Tom.Heknow the answer.
—I put the bike here? —No,you can’t.
—Who is knocking at the door? —It be Miss Zhang.Because she has just gone to Japan.