20. I am afraid you will have to walk home on foot . 恐怕你不得不步行回家了。
21. I am afraid you can\'t avoid do some washing by yourself . 恐怕你逃避不掉自己洗衣服了。
22. I think it necessary for you to obey the rules . 我看你有必要服从规章制度。
23. It is for you to decide whether to go or to stay . 是去是留由你决定。
24. There\'s no reason why you should pull down that fence . 没有理由一定要你拆掉那个篱笆。
25. It is up to you decide . 由你决定。
26. Please leave it alone . 请别理它 。
27. You had better not pick the flowers . 你最好别摘这些花。
28. I feel it is my duty to give you a hand . 我感到帮助你是我的职责。
29. No , I mustn\'t be late for class once more . 不， 我决不能再迟到。
30. No , I shouldn\'t tell him a lie . I had better not object to his suggestion . 不，我不应该对他说谎。我最好不反对他的建议。
从以上 30 句可以看出，在提示对方的职责中常用情态动词 must , should , need , have to , had better , ought to , don\'t have to 以及 be supposed to do , be necessary to do 等。
● Model Dialogues 交际示范
A
Monitor：Who is on duty today ?
Yu Fang：I am .
Monitor：Class will begin in a minute . You should clean the blackboard .
Yu Fang：Sorry , I nearly forgot it . I\'ll do it at once .
Monitor：You have to remember this next time .
Yu Fang：Yes , I will .
B
Receptionist：Can I help you ?
Guest：Are there any free beds ?
Receptionist：Sure . What kind of room do you like ?
Guest：A single room with a bath .
Receptionist：OK. But you have to fill in this form first .
Guest：Is it necessary ?
Receptionist：Yes , we should also see your ID (身份证) card .
C
Doctor：Well , Mrs Smith , I\'ve completed my examination and I\'m happy to say it\'s nothing serious .
Mrs Smith：Don\'t you think I should take an X - ray ?
Doctor：I don\'t think an X-ray is necessary for this illness .
Mrs Smith：Will I need a blood transfusion ?
Doctor：No , Mrs Smith , you won\'t need it .
Mrs Smith：Shouldn\'t I stay in bed for the rest of the week ?
Doctor：No , you should get outdoors more and get plenty of exercise .
Mrs Smith：Can I be cured ?
Doctor：You should listen to my advice and I\'m certain you\'ll be fine .
Mr Smith：What should I do ?
Guest：You should put this medicine on your arms every four hours and by tomorrow it will be all gone . There\'s nothing to worry about .
● 高考试题缩影
1. — Shall I tell John about it ?
— No , you . I\'ve told him already . ( NMET 94)
A. needn\'t B. wouldn\'t C. mustn\'t D. shouldn\'t
2. — We could have walked to the station ; it was so near .
— Yes . A taxi at all necessary . ( MET 92 )
A. wasn\'t B. hadn\'t been C. wouldn\'t be D. won\'t be
3. There was a lot of fun at yesterday\'s party . You come , but why didn\'t you ? (99 上海)
A. must have B. should C. need have D. ought to have
答案：AAC
B. 单元重点新词透视
1. smooth 作形容词是“光滑的，平静的，平坦的”；作及物动词是“使光滑，消除困难、障碍”。
Our path in life will not always be smooth . 我们的生活道路不会总是一帆风顺的。
This is a smooth meeting . 这是一次顺利的会议。