--Jack, is this your jacket?--No, it _______ be my jacket. My jacket is black but this one is blue.

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

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

— Dad, must we wait until the light becomes green? — Yes, I’m afraid we ______. That’s the traffic rule.

--- ______ I take some photos in the hall ? ---No, you ________.