“Is Jack on duty today?”“It ____ be him. It’s his turn tomorrow.”

According to the air traffic rules, you ___ switch off your mobile phone before boarding.

It _________have rained last night, for the ground is wet.

—What is the result of the survey?—15% of those surveyed worry that in the long term children ________ be more dependent on their parents, which does no good to them.

Should the present unemployment continue, the society________a more troublesome situation.