—Must I go with you?
—No, you ________.

— Are you going to Beijing by air?
— It’s fast, but expensive. So I’m not sure. I _____ take a train.

---Look at the boy running on the playground. Is it David?
---It ______ be him. I saw him go to the teachers’ office just now.

Everyone ______ be polite to the old people.

Kids _________ use the computers to draw in the future.

— May I take the magazine out of the reading room?
— No, you can’t. You ______ read it here. It’s the rule.

-----Can I watch TV, Mom?
-----No, you         . You          to do your homework first.

—Must I come back before supper, mum?
—No, you        .

-- _____ I ask you a question, Mr. Wang?      -- Yes, you _______.

—Listen ! Helen is singing in the next room.
—It __________ be Helen. She is in Tianjin now.