wy人教必修三Unit2healthyeating语法Grammar—情态动词(Ⅱ)分解.ppt

4．在反义疑问句中，常省掉to用oughtnt或shouldnt。 He ought to take back what he has said, oughtnt/shouldnt he? 他应该收回他说的话，是吗？ 2．can/could have done一般用于疑问句和否定句中，表示对过去所发生事情的推测。 He TV last night, for he knew he would have a test. 昨天晚上他不可能看电视，因为他知道就要考试了。 could have done用于肯定句时，表示“本有能力做某事而未做”。 We could have arrived there before dark, but we didnt. 天黑前我们本来能够到那里的，但是没到。 5．neednt have done表示“本不必做某事而实际做了”。 Its so near! We neednt have taken a taxi. 这么近！我们根本没有必要坐出租车。 返回 ②His mother is ill. He has to stay at home to look after her.　 ③I must finish the work before Friday. ④—Need I hand in my paper now? —Yes, you must./No, you neednt. ①By now his restaurant ought to be full of people. ⑤Something terrible must have happened if Li Chang was not coming to eat in his restaurant as he always did. 1.用have to完成句子 ①天色太晚了，我现在得回家了。 Its too late, so I now. ②昨天我不得不离开。 I yesterday. ③你们没有必要担心考试。 You the exam. have to go home had to leave dont have to worry about ④我必须马上做吗？ —Must I do it at once? 不，你不必。 —No, ． 2-2.选词填空：must, mustnt, have to ①现在我不得不走了，因为我妈妈生病了。 I go now, for my mother is ill. ②我一定要戒烟。 I stop smoking. ③晚上你一定不能独自出去。 You go out alone at night. you dont have to have to must mustnt 2．need的用法 1．need 作情态动词, 常用于否定句、疑问句和条件句 。 You neednt come so early. Need I come early tomorrow? [点津]　由need引出的一般疑问句的肯定回答常用must或have to，否定回答常用needn‘t。 2．作为实义动词 You dont need to come so early. Do I need to come early tomorrow? 　 3-1.用need或must完成句子 ①你现在不必去那儿。 You go there now. neednt ②他有必要留在这儿吗？ — he stay here? 是的，他必须。/不，他不必要。 —Yes, he ．/No, he ． must neednt Need 我们不必告诉他真相。 We dont need to tell him the truth. We needn’t tell him the truth. 3、ought to的用法 1．ought to“应该”。与should相比较ought to语气重，偏重“责任、义务、道德、法律”等方面，意为“应该”。