虚拟语气讲解

导读：　　虚拟语气讲解　　下面是www chinazhaokao com中国招生考试网小编整理的虚拟语气讲解，供大家参考!　　英语中if 从句有两种：一种是以陈 ...

　虚拟语气讲解

　　下面是www.chinazhaokao.com中国招生考试网小编整理的虚拟语气讲解，供大家参考!
　　英语中if 从句有两种：一种是以陈述语气叙述的叫做真实条件句，说明所提出的假想是可以实现的;另一种是以虚拟语气叙述的，叫非真实条件句，说明所提出的假想实现的可能性极小或与事实相反。这种虚拟语气一般因所指的时间的不同而分三种情况：
　　⒈ 表示与现在事实相反：
　　If + 从句主语 + 动词的过去式…，主语+should/ would/ could/ might + 动词原形…
　　(be 一般用were)
　　如：
　　①If I were you, I would go by plane.
　　如果我是你，我将坐飞机去。( In fact I am not you. )
　　②If he were here, he would decide what to do.
　　如果他在这里，他会决定做什么。(In fact he isn’t here.)
　　③If I had the letter at hand, I would read it.虚拟语气讲解
　　如果我手头有这封信的话，我会读它的。(In fact I don’t have the letter at hand.)
　　④If she knew about it now, she would come.
　　如果她现在要是知道这件事的话，她会来的。(In fact she doesn’t know about it.)
　　⑤If he had time, he would go with you.
　　如果他有时间，他会同你一起去的。(In fact he is very busy, so he can’t go with you.)
　　⒉ 表示与过去事实相反：
　　If + 从句主语 + had + 过去分词…，主语+should/ would/ could/ might +have +过去分词…
　　如：
　　①If he had come here yesterday, I should have told him.
　　如果他昨天到这里来，我早就告诉他了。
　　(Fact: He did not come and I did not tell him.)
　　②If I had taken his advice, I wouldn’t have made such a mistake.
　　如果我当时接受了他的劝告，我是不会犯那样一个错误的。
　　(Fact: I didn’t take his advice and I made such a mistake.虚拟语气讲解)
　　③If I hadn’t been so busy last Monday, I would have called her.
　　如果我上周一不忙的话，我早就给她打电话了。
　　(Fact: I was busy last Monday and I didn’t call her.)
　　⒊　与将来事实可能相反：
　　①动词的过去式…，
　　If + 从句主语 + ②should +动词原形…， + 主语 + should/ would/ could/ might + 动词原形…
　　③were to +动词原形…，
　　如：
　　①If it should snow/snowed/were to snow tomorrow, I would not go out.
　　如果明天下雪的话，我就不出去了。
　　(But I know it won’t snow tomorrow.)
　　②If he failed/should fail/were to fail, he would try again.
　　如果他失败的话，他会再试一次。
　　(I know that most probably he won’t fail.)
　　③If I had time next year, I would study German.
　　如果我明年有时间的话，我就学德语。
　　(I know that most probably I won’t have time next year.)
　　◆ 在书面语中，有时if虚拟从句可使用倒装形式，方法是：如果if从句中含有were, had 或should时，把条件从句中的if省略，将were/ should/ had 移至主语之前。
　　如：
　　①If I were in his place, I should learn to drive.
　　→ Were I in his place, I should learn to drive.
　　如果我处于他的地位，我一定学开车。
　　②If it should snow tomorrow, the meeting would be put off.
　　→ Should it snow tomorrow, the meeting would be put off.
　　如果明天下雪，会议将会延期。
　　③If they had helped us, we would have succeeded.
　　→ Had they helped us, we would have succeeded.
　　如果他们帮助了我们，我们早就成功了。
　　④If it were to snow tomorrow, what would you do?
　　→ Were it to snow tomorrow, what would you do?
　　万一明天下雪的话，你怎么办。
　　◆ 如果从句和主句所表示的动作发生的时间不一致，例如：一个与过去事实相反，另一个与现在事实相反，动词的虚拟语气形式应根据所指的实际时间来选用。
　　如：虚拟语气讲解
　　①If he were alive, he might have finished his scientific researches on the bridge-building three years ago.
　　如果他现在还活着，他可能三年前就完成了他的桥梁建筑科研工作了。
　　(从句所表示的动作与现在事实相反，主句所表示的动作与过去事实相反)
　　②If you had followed his advice, you would not be in trouble now.
　　如果你当初听从他的建议，你现在就不会陷入这种困境了。
　　(从句表示的动作与过去相反，主句所表示的动作与现在相反)
　　③If I had followed the doctor’s advice, I would be quite all right now.
　　如果我当时听从了医生的建议，我现在就完全恢复了健康。
　　(从句所表示的动作与过去相反，主句所表示的动作与现在相反)
　　④If I were you, I would have gone with her.
　　如果我是你，我早就和她一起去了。
　　(从句表示与现在事实相反，主句所表示的动作与过去事实相反)
　　◆ 有时假设的情况并不以条件从句表示出来，而是通过一个介词短语来表示
　　如：
　　①We could have done better under more favourable conditions.
　　在更有利的条件下，我们还可以做得更好些。
　　②Without the warmth and light of the sun, the earth’s vegetation would die almost immediately.
　　如果没有太阳的热量和光，地球上的植物几乎会马上死去。
　　◆ 假设的情况有时可以通过上下文或其他方式来表现：
　　如：
　　①I was ill that day. Otherwise I would have taken part in the sports meet.
　　我那天生病了，否则就参加运动会了。
　　②But for the storm, we should have arrived earlier.
　　要是没有碰到暴风雨，我们还会早一些到的。
　　③I would have written before, but I have been ill.
　　本来该早就给你写信的，但我生病了。
　　㈡ 虚拟语气在wish后的宾语从句中的应用：
　　wish 的各种时态都不影响从句的时态
　　⒈ 与现在事实相反的愿望：
　　wish + 从句主语+ 动词的过去式
　　如：
　　①He wishes he were a bird.
　　他希望自己是一只小鸟。
　　②I wish I were ten years younger.
　　真希望自己年轻十岁。
　　③I wish I remembered the address.
　　我要是记得地址就好了。
　　⒉ 与过去事实相反的愿望：
　　wish + 从句主语+ had + 动词的过去分词
　　如：
　　①She wished she had been braver then.
　　她真希望那时她胆子大一些。
　　②I wish he had gone to the exhibition.
　　要是他去参观展览会就好了。
　　③I wish you had been here yesterday.
　　要是你昨天在这里就好了。
　　④We wish we had paid more attention to our pronunciation.
　　但愿我们过去对发音注意得更多一些。
　　⒊ 与将来事实可能相反的愿望：
　　wish + 从句主语+ should/would/could/might + 动词原形
　　如：
　　①We wish that he could be with us tomorrow.
　　但愿他明天和我们在一起。
　　②I wish he would try again.
　　我希望他还能再试一次。
　　㈢ 虚拟语气在suggest, demand, propose, command, request, desire, order, insist等动词之后的宾语从句中，表示命令和建议：
　　suggest/ demand/ propose/ command/ request/ desire/ order/ insist/ask(请求，要求)+(that) + sb.+ (should ) +动词原形
　　如：
　　①We suggest that the meeting (should) be postponed.
　　我们建议会议延期。
　　②They insist that he (should ) obey every command.
　　他们坚持他该服从命令。
　　③The chairman proposed that they (should) stop the meeting.
　　主席建议他们把会议停下来。
　　④The leader ordered the soldiers (should) be sent to the front at once.
　　那位领导人下令马上派兵上前线。
　　⑤They asked that arrangements (should) be made to send the comrades back to Beijing.
　　他们要求作好安排把这些同志送回北京。
　　⑥The workers demanded that their wages (should) be increased.
　　工人们要求增加工资。
　　◆suggest的主语如果不是指人，而是指某一现象时，其后的宾语从句常不表示建议，而是暗示一种情况，此时的宾语从句中不用虚拟语气(sb. should do sth. ), 而应根据内容使用正确的时态。
　　如：
　　I suggested that the meeting (should) not be put off in spite of the rain.
　　我建议不要因为下雨而推迟会议。
　　The look on her face suggested she was sad.
　　她脸上的表情表明她难过。(was不能改成should be)
　　◆如果insist后面的宾语从句不是表示对未来某一动作的主张或要求，而是坚持过去或当时的某一事实，则其宾语从句不用虚拟语气(should do sth.), 而应根据内容使用正确的时态。
　　如：
　　He insisted we discuss the problem at the meeting.
　　他坚持在会议上我们要讨论这个问题。
　　He insisted he hadn’t spoken ill of you behind your back.
　　他坚持说他没有在背后说你的坏话。
　　㈣ 虚拟语气在as if/though 从句中的应用：
　　在as if/though引导的从句中，如果谈论的是不可能或不真实的情况，它们所引导的表示虚拟性比喻或方式的状语从句要用虚拟语气。动词形式和wish后面的从句中动词形式变化相同。
　　如：
　　①I have loved you as if you were my son.
　　我喜欢你，就好像你是我的儿子。
　　②They were sitting there as if nothing had happened.
　　他们只是坐在那里就像什么事都没发生过。
　　③They are talking as if they had been friends for years.
　　他们说话很亲热就像多年的老朋友。
　　④I heard a noise as if someone were breathing.
　　我听到了声音就像有人在呼吸。
　　(as if从句的虚拟语气用进行时态表示与主句的动作同时发生
　　◆as if/though 引导的从句有时依句意需要，也可用陈述语气，表示说话人认为有可能是事实的事
　　如：
　　①It seems as if she knows me.
　　似乎她认识我。(事实上她认识我的可能性很大)
　　②He walks as if he is drunk.
　　他走起路来像是喝醉了酒。(事实上他可能真的喝醉了)
　　㈤ 虚拟语气在It’s (high) time…中的应用：
　　It’s (high) time that sb. +动词过去式/ should do sth.
　　如：
　　①It’s time that we went/should go to bed.
　　我们该睡觉了。
　　②It’s high time that we stopped/should stop this practice.
　　我们的确该停止这种做法了。
　　㈥ 虚拟语气在so that, in order that引导的目的状语从句中的应用：
　　一般多用may 或might(口语中也可用can/could)
　　如：
　　①Speak clearly so that they may understand you.
　　请说得明白些，以便他们都能懂你的话。
　　②I lent them some money in order that they might go for a holiday.
　　我借给他们一些钱以便他们可以去度假。
　　㈦ 虚拟语气在for fear that, lest 和in case引导的从句中的应用：
　　这时谓语动词多用should加动词原形
　　如：
　　①I took my umbrella with me lest it should rain.
　　我带上雨伞怕下雨。
　　②He burned all the important documents for fear that they should fall into the enemy’s hands.
　　他把所有的重要文件都烧毁了，怕它们会落入敌人的手中。
　　③Here’s some money in case you should need it.
　　这儿有点钱以防你需要用。
　　㈧ 虚拟语气在某些表语从句和同位语从句中的应用：
　　在suggestion, proposal, order, plan, idea, request等词后面的表语从句和同位语从句中，常用：(should) +动词原形，用来适合于说话人所表示的建议、要求、命令等语气。
　　如：
　　①Her suggestion is that we should go to help them.
　　她的建议是我们理应去帮助他们。(表语从句)
　　②The officer’s order was that the bridge be destroyed before daylight.
　　军官命令在拂晓前炸毁桥梁。(表语从句)
　　③My idea is that we send a few comrades to help the other groups.
　　我的意见是派几个同志去帮助别的小组。(表语从句)
　　④What do you think of his proposal that we should put on a play at the English evening?
　　他建议在英语晚会上演一个剧，你觉得怎么样。(同位语从句)
　　⑤I agree with the plan that she visit London this summer.
　　我同意她今年夏季出访伦敦。(同位语从句)
　　⑥The advice that steps be taken at once sounds reasonable.
　　立即采取步骤的建议听起来有道理。(同位语从句)
　　㈨ 在It is important/natural/necessary/strange that…的主语从句中：
　　(should ) + 动词原形
　　如：
　　①It is important that we (should) unite with all that can be united in the struggle.
　　在斗争中团结一切可以团结的人是非常重要的。
　　②It is necessary that I (should) return the book this morning.
　　今天早上我有必要还书。
　　③It is strange that she (should) go away without saying good-bye.
　　奇怪的是她不说再见就走了。
　　④It was quite natural that my picture (should) surprise them.
　　我的照片使他们吃惊是十分自然的。
　　㈩ 在It is suggested/required/desired/ordered/proposed…that…和It’s a pity that…的主语从句中：
　　(should) + 动词原形
　　如：
　　①It is requested that he give a performance at the party.
　　有人请求他在聚会上表演一个节目。
　　②It has been decided that the meeting be postponed till next Saturday.
　　已经决定会议延期到下周日。
　　③It is desired that we should get everything ready by tonight.
　　希望一切在今晚准备好。
　　④It is a pity that he should be so conceited.
　　真遗憾他会这样自高自大。
　　(十一) 在expect, believe, think等动词的否定形式后的宾语从句中，用should + 动词原形/ 完成形式，表惊奇、怀疑等语气
　　如：
　　①I never expected that the problem should be so complicated.
　　我从没想过这个问题会这样复杂。
　　②I never thought he should refuse.
　　我从没想到他会拒绝。
　　(十二) 在if only 引导的句中：
　　如：
　　①If only I had not lost it.
　　我要是没丢多好呀。
　　②If only we had taken his advice.
　　我们要是听从了他的建议就好了。
　　③If only the letter had arrived in time.
　　信要是及时到就好了。
　　④If only he were here.
　　要是他在这里就好了 。
　　(十三)在某些表示祝愿的句子中：虚拟语气讲解
　　谓语动词用动词原形
　　如：
　　①Long live the Communist Party of China!
　　中国共产党万岁!
　　②May the friendship between our two peoples last forever.
　　祝两国人民的友谊万古长青。
　　③May you succeed!
　　祝你成功!
　　(十四)情态动词的过去式用于现在时态，表示说话人客气、有礼貌或语气婉转
　　如：
　　①Would you mind my smoking here?
　　我在这里吸烟你介意吗?
　　②Could you come a little earlier next time?
　　下次你稍微早点来好吗?
　　③You had better leave the matter to me.
　　你最好把这事交给我。
　　(十五)在even if 引导的让步状语从句中，表示一种假设，构成虚拟语气，其虚拟语气构成形式与if虚拟条件句相同
　　如：
　　①Even if he had been tended without delay, nothing would have saved him.
　　即使他受到立即治疗，也没有什么东西能救他。
　　②Even if I were there, I shouldn’t be able to solve the problem by myself.
　　即使我在那儿，我也不能自己解决这个问题。
　　高考预测题：
　　1. If I ________ where he lived, I _______ a note to him.
　　A. knew, will send
　　B. had known, would have sent
　　C. know, would send
　　D. knew, would have sent
　　2. Alice is ill today. If she ________, she _______ absent from school.
　　A. were not ill, would not be
　　B. had been ill, would not have been
　　C. had been ill, should have been
　　D. had not been ill, could be
　　3.Without your help, we _______ so much.
　　A. won’t achieve　B. didn’t achieve　　 C. don’t achieve　　 D. wouldn’t have achieved
　　4.We wish we _______ what you did when we were at high school.
　　A. did　　　　 B. had done　　　　 C. have done　　　　　　 D. should do
　　5.He asks that he ______ an opportunity to explain why he’s refused to go there.
　　A. is given　　 B. must give　　 C. should give　　　　 D. be given
　　6.Father demanded that we ________ home as soon as the school is over.
　　A. might return　　 B. must return　　 C. should return　　　　 D. ought to return
　　7.Peter insisted that he __________ anything at all.
　　A. had not stolen　　 B. should not steal　　 C. doesn’t steal　　 D. steal
　　8.If only I _______ to the lecture!
　　A. listen　　　　 B. will listen　　 C. am listening　　　　 D. had listened
　　9.If you had enough money, what __________ ?
　　A. will you buy　B. would you buy　 C. would you have bought　　D. will you have bought
　　10.Her tired face suggested that she ______ really tired after the long walk.
　　A. had been　　　　 B. was　　　　　　 C. be　　　　　　 D. should be
　　11.He didn’t know my telephone number, otherwise he ________ me.
　　A. had telephoned　　 B. would telephone　　 C. would have telephoned 　D. telephone
　　12.----Why didn’t he buy the book?
　　----He _______, but his mother _____ allow him.
　　A. would , didn’t
　　B. would have, didn’t
　　C. had had, wouldn’t
　　D. had bought, hadn’t
　　13.----Do you mind if I close the door?
　　----Well, I’d rather you ________.
　　A. don’t　　　　 B. didn’t　　　　　　 C. won’t　　　　 D. mustn’t
　　14.It’s time that we ________ the problem.
　　A. must solve　　 B. can solve　　　　 C. solved　　　　 D. have solved
　　15.But for that heavy rain, we _____ a pleasant journey.
　　A. would have had　　 B. would not have had　　 C. will have　　 D. will not have
　　16._______ today, I would get there in three day.
　　A. If I am leaving　　 B. Were I to leave　　 C. If were I to leave　　 D. If I leaves
　　17.If my teacher ________ fixing the radio, he would have brought it back to me.
　　A. was able to finish
　　B. could finish
　　C. had been able to finish
　　D. would be able to finish
　　18.I should very much like ______ but you didn’t invite me.
　　A. to go to the party
　　B. to have gone to the party
　　C. going to the party
　　D. having gone to the party
　　19.Without my help, he ______ such rapid progress.
　　A. couldn’t make　 B. wouldn’t make　 C. will not have made　 D. wouldn’t have made
　　20.I would have come earlier, but I _______ that you were waiting.
　　A. wouldn’t know　　 B. hadn’t known　　 C. didn’t know　　　　 D. haven’t known
　　21.Tom is looking for his key. ______he put the key in his desk, he ______.
　　A. If, will not lose　　 　B. If, wouldn’t have lost
　　C. Had, wouldn’t lose　　 D. Had, wouldn’t have lost
　　22.If it _______ Sunday tomorrow, I would go to the theatre.
　　A. is　　　　 B. will be　　 C. were　　　　D. were to
　　23.The teacher’s advice is that children ________ every evening.
　　A. will not watch TV　　 B. not watch TV　　 C. don’t watch TV　　 D. needn’t watch TV
　　24.It is strange that he ______ you this.
　　A. would tell　　　　 B. should tell　　　　 C. has told　　　　 D. had told
　　25.If there were no homework to do, we should have _______.
　　A. much happier time B. a much happier time　　 C. a more happier time D. much happy time
　　26.I noticed that my grandmother was very upset when I told her about the accident, so I wished I ______ it to her.
　　A. had not mentioned　　 B. did not mention　　 C. have not mentioned　　 D. do not mention
　　27.My father and mother insisted that I ______ home.
　　A. stayed　　 B. could stay　　　　 C. has stayed　　　　 D. stay
　　28.Our teacher hasn’t come yet. If he ______ on time, we would have to put off the meeting.
　　A. should come　　 B. would come　　 C. shouldn’t come　　　　 D. doesn’t come
　　29.He sat there, lost in thought, as if he _____ for ever his power of judgement.
　　A. had lost　　　　 B. lost　　　　 C. has lost　　　　 D. lose
　　30.If she hadn’t sold her hair, she ______ the gold watch for Jim.
　　A. wouldn’t buy　　 　　B. would have bought
　　C. could have bought　　 D. couldn’t have bought
　　答案与提示：
　　1.B　　表示与过去情况相反的虚拟结构。题意为：如果我曾知道他住在哪里的话，我会给他寄封信的。
　　2.A　　由句中的“Alice is ill today.”可知本小题的空白处应填入表示与现在情况相反的虚拟结构。题意为：玛丽今天生病了，如果她没生病的话，她不会缺课的。
　　3.D　　“Without your help”实际上相当于一个虚拟条件句，在此句中表示与过去相反的虚拟条件句。Without your help= If you hadn’t helped us.题意为：如果没有你的帮忙的话，我们不会取得这么多的成就。
　　4.B　　 wish后面的宾语从句中谓语动词要使用虚拟语气。“…what you did when we were at high school.”暗示在本小题的空白处应填入表示与过去情况相反的虚拟结构。题意为：我们多么愿在中学读书时能够做过你曾做过的事情呀。
　　5.D　　在ask(要求)后面的宾语从句中，谓语动词也常用虚拟语气形式：(should) + 动词原形。题意为：他要求给他个机会来解释他拒绝到那里去的理由。
　　6.C　　在demand(要求)后面的宾语从句中，谓语动词也常使用虚拟语气形式：(should) +动词原形。题意为：父亲要求我们一放学就回家。
　　7.A　　 当动词insist 的意思是“坚持说”时，其后面的宾语从句中不使用虚拟语气结构。题意为：彼得坚持说他没偷过任何东西。
　　8.D　　 在if only引导的句中常使用虚拟语气。这种虚拟结构与虚拟条件句里谓语形式相同。题意为：要是我听过那个讲座或好。
　　9.B　　 本句为对现在情况虚拟，主句为would, should(第一人称)，could等加动词原形。
　　10.B　 suggest意为“建议”时，后面，的宾语从句要用should+动词原形，但在本题中suggest意为“说明”，“暗示”，其宾语从句的动词按正常情况处理，故不选C D; A项时态不符合题意。
　　11.C　　 这是一个暗示条件的对过去情况虚拟的句子，前句暗示“if he had known my telephone number…”后面主句是would + 完成时，A、B、D三项都不符合题目要求。
　　12.B　　 答语中为对过去虚拟的主句，“本来会买的”，would have =would have bought， but后面是过去的事实。
　　13.B　　 I’d rather接从句，动词一般要用过去时，这是虚拟语气的一种情况，表示一种希望。A、C、D三项都不合题意。
　　14.C　　 It’s time后面的宾语从句中，通常要用动词的过去时表示一种虚拟语气，即：It’s (high) time that sb. +动词过去式/ should do sth。
　　15.A 　　由前置状语中but for“倘若没有”，“若不是”推知，主句为一虚拟语气，而且是对过去情况的假设。题意为：如果没有那场大雨，我们的旅途会是愉快的。
　　16.B　　 本题为对将来情况的虚拟条件句：虚拟语气讲解
　　If + 从句主语 + 动词的过去式
　　should +动词原形
　　were to +动词原形…。
　　还可以把were提到主语的前面，此时要把连词if省略。
　　17.C　　这是个对过去情况虚拟的主从句子，条件句过去完成时，主句为情态动词的过去时，加上完成时，这个句子乍看起来是区别could和be able to的用法，其实不然，填A、B、D句子的语法意义不通。
　　18.B　　 本句中I should very much like to的句法功能相当于would，接动词的完成体表示“本来非常想，而没有”是一种对过去情况的虚拟，but 后面的句子给出了“没有做到…”的原因，暗示“如果邀请的话…”。A项的时态不是对过去事情的虚拟，应排除;C、D两项为动名词短语，不应当接在like的后面。
　　19.D　　 这是一句对过去事实进行假设的虚拟语气的句子，without my help相当于If he hadn’t had my help, 因为主句应当用情态动词的过去式带动词的完成体形式，A、B两项应予排除，C项为将来时，并不能使上下文意义通。题意为：如果没有我的帮助，他不会取得如此快的进步。
　　20.C　　主句为对过去事实相反的推测，but后面说的是真实的事实，但隐含“如果我知道…”的意思;A、D两项时态不符，所填的时态应与主句相呼应，由but转成陈述语气，故but后面“I”引起的句子应为真实的情况，故用一般过去时。
　　21.D　　　题意为：假如他把钥匙放在课桌里的话，就不会丢钥匙了。这是对过去情况的虚拟语气：If…had +过去分词…, …would have +过去分词…。 Had he put the key in the desk= If he had put the key in the desk。
　　22.C　　 本题是对将来时间的虚拟，故A、B不对;D项were to后面应有be。
　　23.B　　 在suggestion, proposal, order, plan, idea, request等词后面的表语从句和同位语从句中，常用虚拟语气： (should) +动词原形，用来适合于说话人所表示的建议、要求、命令等语气。其否定形式为：(should) + not +动词原形。
　　24.B　　 It is strange (important, necessary, important等)后面的所接的that句为：…should +动词原形。
　　25.B 　　本题为对现在情况的虚拟语气。A项没有冠词，不对;C项犯双重比较的错误;D项中，much不修饰happy的原级形容词。
　　26.A　　 wish后面的宾语从句中谓语动词要使用虚拟语气。本题表示对过去事情的虚拟，故用过去完成时形式。
　　27.D　　主句的谓语动词insist表示“要求某人…”时，后面应用虚拟语气：(should)+动词原形。这样的词还有： request, demand, order, suggest等。
　　28.C　　 本题是对将来情况进行的虚拟语气。条件从句用should +动词原形。
　　29.A　　 as if 此处为虚拟语气，是对过去情况的虚拟，故用过去完成时。
　　30.D　　题意为：如果她不卖掉自己的头发的话，她就不能给吉姆买金表了。这是对过去情况虚拟的主从句，主句应用情态动词的过去式+完成体的动词。

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