（一)情態(tài)動詞
一．情態(tài)動詞的現(xiàn)在完成式的用法
情態(tài)動詞現(xiàn)在完成式主要有兩個功能：表示已經(jīng)發(fā)生的情況和表示虛擬語氣醫(yī)學全在線m.payment-defi.com。在這兩個方面must/mustn’t,;can/cann’t;need/needn’t;may/mayn’t;might/mightn’t;should/shouldn’t;ought等情態(tài)動詞＋完成式表示的意思是有一定區(qū)別的
1．表示已經(jīng)發(fā)生的情況。
1)must have+過去分詞，表示對已發(fā)生情況的肯定推測，譯為“（昨天)一定……”。如：
My pain apparent the moment I walked into the room, for the first man I met asked sympathetically:” Are you feeling all right?”
[A] must be [B] had been [C] must have been [D] had to be
（答案為C)
2)can’t / couldn’t have+過去分詞，表示對已發(fā)生情況的否定推測，譯為“（昨天)一定沒……”。如：
Mary my letter; otherwise she would have replied before now.
[A] couldn’t have received [B] ought to have received
[C] has received [D] shouldn’t have received
（答案為A)
3)may / might have +過去分詞，表示對已發(fā)生的事情做不肯定、可能性很小的推測，或事實上根本沒發(fā)生，譯為“也許……”。如：
At Florida Power’s Crystal River plant, a potentially serious leakage of radioactive water may have been unknowingly caused by an electrician.
2．表示虛擬語氣。
1) needn’t have + 過去分詞，表示做了不必做的事，相當于”didn’t need to do”,譯為“其實沒必要……”。如：
You needn’t have come over yourself.
As it turned out to be a small house party, we so formally.
[A] needn’t dress up [B]did not need have dressed up
[C] did not need dress up [D] needn’t have dressed up
(沒有必要穿的那么正式，體現(xiàn)是說話者的建議，實際結(jié)果是否真的穿的很正式?jīng)]有確定，答案為D)
2)should have +過去分詞，表示應(yīng)該做某事但實際上未做，譯為“本應(yīng)該……”should not + have過去分詞表示本不應(yīng)該做某事但實際上做了，譯為“本不應(yīng)該……”。如：
I regret having left the work unfinished; I should have planned everything ahead carefully.
我本來應(yīng)該事先認真地把每件事情規(guī)劃的很好，但實際上作者還是沒有規(guī)劃好，以至工作沒有完成。
3) ought to have +過去分詞，表示動作按理該發(fā)生了，但實際上未發(fā)生，譯為“該……”，與should 的完成式含義類似。如：
Ｔhe porter ought to have called the fire-brigade as soon as he saw the fire in the stock, which went up in smoke .
4) could have +過去分詞，表示過去本來可以做但卻未做，譯為“完全可以……”。這點與ought/should/ have +過去分詞用法相似。如：
What you said is right, but you could have phrased it more tactfully.
5) may/ might have +過去分詞，表示過去可以做但實際未做，譯為“（那樣)也許會……”。如：
It might have been better to include more punchy statistics and photos of equipment in the introduction to further assist first-time office automation managers.
二．幾個情態(tài)動詞�？嫉木湫停�
1)．may/might (just) as well “不妨，最好”，與had better相近；
Since the flight was cancelled, you might as well go by train.
既然航班已經(jīng)取消了，你不妨乘火車吧。相當于you had better go by train。
2) ．cannot / can’t…too …“越……越好，怎么也不過分”。注意這個句型的變體cannot…over….如：
You cannot be too careful when you drive a car.駕車時候，越小心越好。
The final chapter covers organizational change and development. This subject cannot be over emphasized .
3) ．usedn’t 或did’t use to 為used to (do) 的否定式。
4)．should 除了“應(yīng)該”一層意思外，考研大綱還規(guī)定要掌握其“竟然”的意思。如：I didn’t expect that he should have behaved like that. 我無法想象他竟然這樣做醫(yī).學全在線提供m.payment-defi.com。
三．情態(tài)動詞被動關(guān)系的主動表達法
1． want, require, worth（形容詞)后面接doing也可以表示被動意義。
Your hair wants cutting
The book is worth reading
The floor requires washing.
2．need既可以用need to be done 也可以使用need doing ，兩種形式都表達被動的意義
The house needs painting= the house needs to be painted.
The watch needed repairing= the watch needed to be repaired.
