About _____ of the world population is Chinese.

______do you sleep every night? —Six to eight hours. [ ]

Listen! David is talking happily with his mother in the next room.　— It ______ be his mother. She has gone to Yunnan to be a volunteer doctor.

I feel so nervous before the exam that I can’t sleep well at night. — I think having a holiday will_______ help you relax.

Must I stay here with you?– No, you ______. You may go home, but you _____ go to the net bar(网吧).