___ is known to all, China will be an _____ and powerful country in 20 or 30 years’time.

Oh, boy, why are you just playing games all day? Can't you find something ______ doing at all?

Do remember to be________. We must avoid any possible risks when doing this dangerous chemical experiment—burns, poisonous gases or cuts from broken tubes.

_______she is not so cheerful________she used to be?

Chen Yifei(1946－2005)，who died in his ________ fifties，was ________ successful artist.