16. 能力Ability
　　I can ....
　　He is able to ....
　　17. 肯定和不肯定 Certainty and uncertainty
　　a.I'm sure (of that).
　　I'm sure (that) ....
　　b.I'm not sure (of that).
　　I'm not sure whether/if . . . .
　　c.Perhaps/Maybe.
　　18. 禁止和警告 Prohibition and warnings
　　a.You can't/mustn't . . . .
　　If you ... , you'll....
　　You'd better not do it.
　　Don't smoke!
　　Don't be late!
　　b.Look out!
　　Take care!
　　Be careful!
　　19. 可能和不可能 Possibility andimpossibility
　　He can/may . . . .
　　It is possible that . . . .
　　It is impossible that . . . .
　　20. 预见、猜测和相信 Prediction, conjecture and belief
　　a.He will . . . .
　　b.It seems (that) ....
　　c.I believe that he is right.