I know you have eaten all sorts of junk food your mother and I probably _____ you have.

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

 Sorry, I’m late. I ____ have turned off the alarm clock and gone back to sleep again.

—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?

The train is to start soon and Mary hasn’t turned up． What _____ have happened to her?