81.You mustn't speak to your mother like that, ______ you?
A. should B. must C. may D. dare
82.---Do you smoke? ---_______. It's two years since I smoked.
A. No, I don't B. Yes, I do C. Not too much D. Oh, yes ,but I wish I didn't
83.Selecting a mobile phone for personal use is no easy task because technology ____so rapidly.
A. is changing B. has changed C. will have changed D. will change