—There's someone knocking on the door．Who        it be?—It must be Mary．She promised to be here at 8：00．

—Look! Is that Mr. Green?—It          be Mr. Green. He has gone to Shanghai.

— Simon, when are we going to have a class meeting this week?— Sorry. Ask our monitor, please. He         know.

---Can you drive a car? --- No, I ________. I’m not old enough to get a license.

Susan’s parents bought a large house with a swimming pool. It ______be very expensive.