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T:Congratulations!Do you know how to use “need”? S2:I think in negative sentences,“don’t need to”,“needn’t” or “don’t have to” is used to say that there is “no necessity”. T:Please give me an example.OK? S2:I know the reason why you were late.You needn’t try to explain. T:Thank you.In addition,I want to tell you “have got to” is used instead of “have to” in informal English.Is that clear? Ss:Yeah. T:Now look at the blackboard.(Write the following on the blackboard.) 1.It must have rained last night,for the ground is wet. 2.You can’t have seen him yesterday,for he is still in Australia. 3.You could have told me he was coming. 4.She is very late.She may have missed the bus. T:These sentences have something in common.Who can tell me what it is? Ss:The modal verbs in these sentences are used together with perfect infinitives. T:Very good.Then let’s review the modal verbs used together with perfect infinitives. S3:When should we use modal verbs together with perfect infinitives? T:When we talk about the past,we can use the structure,but it has a special meaning.It is used for speculating(thinking about what possibly happened) or guessing (thinking about how things could have been different).Have you got it? Ss:Yes.Thank you. T:Now let’s do some exercises to consolidate the usage of the structure. 1.I told Sally how to get there,but perhaps I ______for her. A.had to write it out B.must be have written it out C.should have written it out D.ought to write it out 2.You didn’t let me drive.If we ______ in turn,you ______ so tired. A.drove;didn’t get B.drove;wouldn’t get C.were driving;wouldn’t get D.had driven;wouldn’t have got (责任编辑：admin) |