(2013·成都一诊)The chairman ________ hold office for five years according to the constitution.

 I’m really tired of Tom because he ______ keep asking silly questions. 

— I regret to say that I          have shouted at you the other day．— Forget it． I was a bit out of control myself．  

--- 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?

—Mum, I’ve been doing my homework for two hours.    I play computer games for an hour? —No, I’m afraid not. You’d better go out for a walk. It does good to your eyes.