---Whose is the pencil box?---It _____ be Tom’s. Look at his name on the cover!

----Whose book is this?----It _______ our geography teacher’s. You see, his name is on it. 

—I’m afraid you missed a fantastic lecture yesterday. How come you were absent from it?—If you _______ know, I asked for a day off and visited a relative of mine in hospital.

"Those responsible for the accident      be punished while those contributing to solving the problems be rewarded," promised the official then and there.

— When shall we meet your cousin at the station?— His plane took off two hours ago, and it        reach at 5 pm.