—Look! The man at the gate ______ be our headmaster. He is always standing there every morning.—No, it ______be him. He is holding a meeting in the office now.

---Is John coming by train?    ---He should, but he ________ not. He likes driving his car.

—How did he get my telephone number?—You ________ it . You told him last week．

—Could I surf the Internet for twenty more minutes, Mum?—Oh, dear, if you________.

 ---_______I come back before five o’clock? ---No, you ________. But you________ be back later than seven o’clock