—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.

Must I wait till you come back?  No, you ______.

－What does the sign over there say?－“No person _______ bring drinks into the student computer pool.”

—Must I finish the paper tonight?    —No, you _______ finish it tomorrow.

--Let’s go to the Tian’anmen Square by taxi. --Oh, it’s not far from here. We_______ take a taxi.