题目内容：

this is 与this's 的区别?在哪些情况下有不同的含义或用法?

优质解答

一、用“情态动词＋have ＋done”结构表示对过去动作的推测,试题中常用过去时态或过去的时间状语给以暗示.情态动词的这一用法可以用 “对立统一”来概括.
1．当试题的前句和后句在动作和意义上相互补充说明,且整个句意在动作和时间上是一个整体时,我们可用“统一”关系来解决这样的试题.常见的结构有：
must have done： 表示对过去动作的肯定推测,常译作“一定做了……”,只能用于肯定句中.其否定形式为can‘t／couldn‘t have done 疑问式为Can／Could...have done?.
could ／might have done：表示对过去发生的动作的可能性推测,常译作“可能做了……”.如：
1) Sorry I‘m late． I ＿＿＿＿＿ have turned off the alarm clock and gone back to sleep again．
A． might B． should C． can D． will
该题前句说明了结果,后句接着说出了产生这种结果的可能性,对前句进行补充说明.分析选项可知本题应选A.
2) My sister met him at the Grand Theater yesterday afternoon, so he ＿＿＿＿ your lecture．
A．couldn‘t have attended
B．needn‘t have attended
C．mustn‘t have attended
D．shouldn‘t have attended
该题前句叙说一个客观事实,后句对前句进行补充说明,分析选项可知C是错误的; 而B、D两项不符合题意.故本题选A.又如：
Jack ＿＿＿＿ yet, otherwise he would have telephoned me．
A．mustn‘t have arrived
B．shouldn‘t have arrived
C．can‘t have arrived
D．need not have arrived （C）
2．当试题的前后句在动作和意义上构成转折关系时,常借助“but, however, instead”等词来表示过去的动作与客观事实不符,这时我们就可以用“对立”关系来解决这样的试题.这种结构常见的有：
should have done ／ ought to have done：表示过去本应该做某事而实际上没有做.
should not have done ／ ought not to have done：表示过去本不应该做某事但事实上却做了.
need have done：表示过去本来有必要去做某事,但事实上没有做.
need not have done：表示过去本来没有必要做某事,但事实上却做了.如：
3) I was really anxious about you． You ＿＿＿＿＿ home without a word．
A．mustn‘t leave B．shouldn‘t have left
C．couldn‘t have left D．needn‘t leave
分析该题前后句之间的关系和语气可知,事实上是 “本不应该离家出走却走了”,故本题选B.
4) I told Sally how to get here, but perhaps I ＿＿＿＿＿ for her．
A．had to write it out
B．must have written it out
C．should have written it out
D．ought to write it out
由句中的连词but可知前后句之间是对立关系,分析题意可知本题应选C.
二、考查情态动词基本用法之间的比较和辨析.最近几年试题中常借助具体的语境来考查考生对那些最常见的情态动词的基本用法的理解和把握,因此在做这样的试题时应认真分析语境中所含的实际意义,并结合情态动词的基本含义和用法做出正确的选择.
5) —Is John coming by train?
—He should, but he ＿＿＿＿＿＿ not． He likes driving his car．
A．must B．can C．need D．may
mustn‘t 表示“禁止、不准”；cannot 表示“不可能”；need not 表示“不必要”；may not 表示“可能不”.分析语境可知本题应选D.
6) —I hear you‘ve got a set of valuable Australian coins．＿＿＿ I have a look?
—Yes, certainly．
A．Do B．May C． Shall D．Should
分析语境可知这是在征求对方的许可,may表示“答应、可以”,语气比较委婉 shall常用于第一、三人称作主语的疑问句中,表示征求对方意见和指示,假如此空用shall,则意为“要（我）看一下吗?”,不符合上下文意思.故本题选B.
7) Mr Bush is on time for everything． How ＿＿＿＿ it be that he was late for the opening ceremony?
A．can B．should C．may D．must
must be 表示肯定的猜测,只能用于肯定句中,由题意可知本题应选A.
8) —Are you coming to Jeff‘s party?
—I‘m not sure． I ＿＿＿＿ go to the concert instead．
A．must B．would C．should D．might
由题意和下句中的 “I‘m not sure” 可知这段对话中存在一种可能性推测,might可以用来表示一种比较委婉的可能性判定,故本题选D.又如：
I should have been there, but I ＿＿＿＿＿ not find the time．
A．would B．could C．might D．should
分析题意可知第二个分句表示过去的某种能力；C 项只表示语气上的可能性,与题意不符.故本题选B.
9) Johnny, you ＿＿＿＿ play with the knife, you ＿＿＿＿ hurt yourself．
A．won‘t; can‘t B．mustn‘t; may
C．shouldn‘t; must D．can‘t; shouldn‘t
mustn‘t 表示“不可以；禁止”,分析题意可知第二个空表示某种可能性,故本题选B.
10) —Will you stay for lunch
—Sorry, ＿＿＿＿＿＿． My brother is coming to see me．
A．I mustn‘t B．I can‘t C．I needn‘t D．I won‘t
分析题意可知因为“我弟弟要来看我”,所以“不能留下”,因此对别人的邀请或要求应给予礼貌的拒绝.A 项表示“禁止”；C项表示“不必要”；而D项表示“不会”,均不符合题意.故本题选B.又如：
—Could I borrow your dictionary?
—Yes, of course you ＿＿＿＿＿．
A．might B．will C．can D．should
11)—When can I come for the photos? I need them tomorrow afternoon．
—They ＿＿＿＿＿ be ready by 1200．
A．can B．should C．might D．need
该题考查情态动词should的基本含义,分析句意可知本题应选B.又如：
The old man is always hunting the lions, so terrible things ＿＿＿＿ happen to him．（上海‘96）
A．might B．would C．should D． could 烠
12)The fire spread through the hotel very quickly but everyone ＿＿＿＿ get out．
A．had to B．would C．could D．was able to
该题考查了could和be able to的区别,二者都可表示过去时间的能力,但假如表示过去成功地做了某事只能使用was ／ were able to do,故本题选D.
13)—Shall I tell John about it?
—No, you ＿＿＿．I‘ve told him already．
A．needn‘t B．wouldn‘t C．mustn‘t D．shouldn‘t
情态动词shall在试题中表示征询对方意见或请求指示.答句暗示 “没有必要了”,故本题选
A