---Could I have some snacks between meals, mum?---No, you __________.

—You look so tired. —Yes. The loud noise upstairs stopped me        the whole night.

---Whose is the pencil box?---It _____ be Tom’s. Look at his name on the cover!

--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?

Nobody knows for sure how dinosaurs died out 65,000,000 years ago. It _______ because of sudden changes of their living conditions.