It has been announced that all the candidates______ remain in their seats until all the papers have been collected.

---Must Jack come to sign his name on the paper?---Yes, he_____ .

 —Must I go to medical school and be a doctor like you, dad?—No, you _______,son. You’re free to make your own decision.

 ---Whose book is this?---It________ be Ning’s because it has her name on it.

It was playing video games that took the boy too much time that he          have spent learning．