Tom’s mother is busy _____ breakfast for Tom.

---Why not wear your miniskirt, Rose? --- Well, my legs are too thick, if you ______ know.

—The research on the new flu virus vaccine is challenging and demanding. Who do you think can do the job?     —_______ my students have a try?

If you ______ smoke, please go outside.

—Is John coming by train.—He should，but he ________ not.He likes driving his car.