這期我們要來學(xué)習(xí)情態(tài)動(dòng)詞+完成時(shí)的用法,當(dāng)然包括了大家最關(guān)心的虛擬語(yǔ)氣.
    1. may和might+ 動(dòng)詞完成式
    此結(jié)構(gòu)用于推測(cè)過去的行為。例如：
    She said that he might have missed the plane.她說他可能誤了航班。
    2. can和could+ 動(dòng)詞完成式
    A. 表示過去能做而沒做的事，有一種對(duì)過去未付諸實(shí)施的事情的惋惜。例如：
    In those circumstances we could have done better.
    在那樣的情況下，我們本來可以做得更好的。(但沒有做得更好)
    B. 推測(cè)過去的某種行動(dòng)。
    Where can /could she have gone? 她可能到哪里去了呢?
    The boy can't have finished reading the book so soon because it is difficult even to an adult.
    這孩子不可能那么快就把這本書讀完的，因?yàn)榧词箤?duì)一個(gè)成人來說，這本書也是相當(dāng)難的。
    Note:
    can't和couldn't+ 動(dòng)詞原形可以用來表示否定推斷。例如：
    He can't be over fifty.他不可能超過50歲。
    3.must +動(dòng)詞完成式
    表示對(duì)過去行為的推斷，具有較大的可能性，意為“一定…，想必…”。例如：
    She must have gone through a lot.
    她一定吃過很多苦。
    Note:
    must+動(dòng)詞原形→對(duì)現(xiàn)在的推測(cè)，must be+現(xiàn)在分詞→對(duì)未來或現(xiàn)在正在進(jìn)行的推測(cè)。例如：
    She looks happy; she must be having a good time.
    4. needn't+動(dòng)詞完成式和didn't need to do
    A. needn't+動(dòng)詞完成式表示一種已經(jīng)做過的但并無必要的行為。例如：
    You needn't have watered the flowers, for it is going to rain.
    你本來不必澆花的，因?yàn)樘煲掠炅恕?但卻澆了)
    We needn't have told him the news because he knew it already.
    B. didn't need (have) to do結(jié)構(gòu)表示沒有必要做某事，實(shí)際上也沒有做。例如：
    I didn't need to clean the windows. My sister did it.
    我不必擦窗，我妹妹擦了。(我沒有擦)
    5. should +動(dòng)詞完成式
    A.此結(jié)構(gòu)的肯定式表示應(yīng)該做的事而沒有做，否定式表示某種行為不該發(fā)生但卻發(fā)生了。例如：
    You should have given her more help.
    你應(yīng)該多給她一些幫助的。(但沒有給)
    B. 表示推測(cè)，意為“可能”，但可能性較小。例如：
    He should have finished the work by now.
    他現(xiàn)在該把工作完成了。(推測(cè))
    C. should / would have thought意為“本以為，本認(rèn)為”。例如：
    A: "Can you type?"
    B: "Certainly."
    A: "Well, I should have thought you wouldn't."
    I should have thought she wouldn't agree.
    我本來認(rèn)為她不會(huì)同意的。
    D. should have thought有時(shí)意為“認(rèn)為，以為”，相當(dāng)于should think，但表示更為委婉、謙遜或不肯定的語(yǔ)氣。例如：
    I should have thought it fairly good.
    我以為它是很不錯(cuò)的。
    E. should have + 過去分詞用于虛擬語(yǔ)氣：
    Had you written him, you should have known the details.
    6. ought to + 動(dòng)詞完成式
    此結(jié)構(gòu)表示某種過去應(yīng)該做而沒有做的事，或被忽略未做的某種明智行為。例如：
    You ought to have returned the book earlier.(還晚了)
    You ought to have refused her at the beginning, but now it is too late.
    Note:
    這里的ought to也可以用should代替。
    Homework:用給出的動(dòng)詞填空,注意要選用正確的助動(dòng)詞和時(shí)態(tài).
    1.The boy____ the book so soon because it is difficult even to an adult. (read)
    2.We___him the news because he knew it already. (tell)
    3.If we had taken the other road, we ____earlier. (arrive)
    4.I _____you might take this into consideration. (think)
    5.You ____ her at the beginning, but now it is too late.(refuse)
    

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