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教学目标：1. 让学生掌握虚拟语气的概念和构成方法。
2. 培养学生正确运用虚拟语气表达假设、愿望、请求等情景的能力。
3. 提高学生的英语写作和口语表达能力。
教学重点：1. 虚拟语气的构成方法。
2. 虚拟语气在不同情景下的运用。
教学难点：1. 虚拟语气在不同时态中的变化。
2. 虚拟语气在实际语境中的运用。
教学准备：1. 教学课件2. 练习材料3. 白板或黑板教学过程：一、导入1. 教师用简短的英语句子，引导学生回顾一般现在时、一般过去时和一般将来时的用法。
2. 提问：同学们，你们知道在英语中还有哪些时态呢？今天我们就来学习一种特殊的时态——虚拟语气。
二、新课讲解1. 教师介绍虚拟语气的概念和构成方法，通过举例让学生了解虚拟语气的基本用法。
2. 讲解虚拟语气在不同时态中的变化，如：现在时、过去时、将来时等。
3. 分析虚拟语气在以下情景下的运用：a. 假设情景：If I were a bird, I would fly to the sky.b. 愿望情景：I wish I could travel around the world.c. 请求情景：Could you please help me with my homework?三、练习巩固1. 教师布置练习题，让学生根据所学知识完成。
2. 练习形式包括：a. 选择题：判断句子是否为虚拟语气，并说明理由。
b. 完形填空：在句子中填入合适的虚拟语气形式。
c. 写作：根据所给情景，运用虚拟语气写一段短文。
四、课堂小结1. 教师总结本节课所学内容，强调虚拟语气的构成方法和不同情景下的运用。
2. 学生分享自己在练习中的收获和遇到的问题。
五、课后作业1. 完成课后练习题。
2. 针对课后作业中遇到的问题，进行自主学习。
教学反思：1. 本节课通过讲解、练习和总结的方式，使学生掌握了虚拟语气的概念、构成方法和不同情景下的运用。
2. 在教学过程中，关注学生的个体差异，针对不同学生的学习需求，给予个性化的指导。
虚拟语气Subjunctive Mood●Function（1）_________________________________（2）_________________________________●Form条件句中有_____，____或____时，如果省略if，则需把_____，____或____放在主语前，构成倒装结构。
e.g. If I were in your position, I would do it.→Were I in your position, I would do it.II.错综时间条件句应的调整。
E.g. If you had worked hard, you would pass the exam this time．(从句指过去，主句指现在)III.含蓄虚拟语气有时，假设的情况并不用条件从句表达，而是暗含在上下文中，由without，but for，otherwise，or等来表达。
E.g. Without electricity, life would be quite different today．(介词)But for your help, we couldn’t have succeeded．(介词短语)I was ill that day. Otherwise, I would have taken part in the sports meeting．(副词)He telephoned to inform me of your plan or I would have known nothing about it．(连词)IV.从句中的虚拟语气1.宾语从句A. 用于表示建议、愿望、命令等动词后的宾语从句中，Sb + v. + 从句。
常见的动词有：demand，order，require，insist，suggest，advise，request，urge，mand，remend等。
人教版五年级英语虚拟语气练习题30题含答案解析1. If I ____ a magician, I would make all the toys come alive.A. amB. wasC. wereD. be答案：C解析：在虚拟语气中，表示与现在事实相反的假设，be动词一律用were，不管主语是第几人称。
A选项am是一般现在时的形式，不符合虚拟语气语法规则。
B选项was虽然是be的过去式，但在虚拟语气中这种用法错误。
D选项be 形式错误。
2. I wish I ____ fly like a bird in the sky.A. canB. couldC. willD. would答案：B解析：wish引导的虚拟语气，表示愿望，与现在事实相反时，动词要用一般过去式，can的过去式是could。
A选项can是一般现在时形式，不符合虚拟语气要求。
C选项will表示将来，不符合此语境。
D选项would用于虚拟语气的从句中，但这里需要的是情态动词的过去式。
3. If he ____ more time, he would play more games.A. hasB. hadC. haveD. having答案：B解析：在虚拟语气的条件句中，如果是与现在事实相反的假设，动词要用一般过去式。
A选项has是一般现在时的形式，不符合虚拟语气语法。
C选项have 形式错误。
D选项having不能作谓语动词。
4. She wishes she ____ a princess in a fairy tale.A. isB. wasC. wereD. are答案：C解析：wish引导的虚拟语气，与现在事实相反时，be动词要用were。
A选项is是一般现在时形式，不符合虚拟语气规则。
B选项was在虚拟语气中这种用法错误。
D选项are与主语she不搭配且不符合虚拟语气要求。
5. If it ____ sunny tomorrow, we would go for a picnic.A. isB. wasC. wereD. be答案：C解析：在虚拟语气中，表示对将来情况的假设（实现的可能性不大），be动词要用were。
六年级英语虚拟语气练习题30题1.If I were the teacher, I ____ give more homework.A.wouldB.willC.shallD.should答案：A。
如果我是老师，这是一种与现在事实相反的假设，要用虚拟语气。
在虚拟语气中，if 引导的条件句用一般过去时，主句用“would/should/could/might+动词原形”。
选项B、C 不是虚拟语气的用法。
选项D“should”在虚拟语气中通常表示“应该”，不太符合这个语境，而“would”更能表示一种假设情况下的“会”。
2.If he had more time, he ____ play basketball with us.A.wouldB.willC.shallD.should答案：A。
如果他有更多时间，这是与现在事实相反的假设，用虚拟语气。
同理，if 引导的条件句用一般过去时，主句用“would/should/could/might+动词原形”。
选项B、C 不是虚拟语气的用法。
选项D“should”在这里不合适。
3.I wish I ____ a bird and could fly freely.A.amB.wasC.wereD.be答案：C。
wish 后面的宾语从句要用虚拟语气。
表示与现在事实相反，be 动词要用were。
选项A、B 不是虚拟语气的用法。
选项D“be”一般在特定的语法结构中才会单独出现，这里不合适。
4.If my mom allowed me, I ____ go to the party.A.wouldB.willC.shallD.should答案：A。
如果妈妈允许我，这是与现在事实相反的假设，用虚拟语气。
主句用“would/should/could/might+动词原形”。
选项B、C 不是虚拟语气的用法。
选项D“should”不太符合语境。
5.I wish I ____ taller so that I could play basketball better.A.amB.wasC.wereD.be答案：C。
虚拟语气(the subjunctive mood)1.划出下列虚拟语气主句和从句的时态，并且辨析与哪个事实相违反1.If I were you, I would go there.2. If Tom were his father, he should seize the chance.3.If he had time, he might attend the meeting.4.If I had met Wanghua, I could have told him5.If I were to go abroad, I would go to America.6. If It should rain, we could call off the meeting7.If It rained, we might cancel the meeting.8. Even if I were busy, I would attend his party.9.Even if I had been busy them, I would have helped you.2.错综条件复杂句。
1.If you had followed my advice, you wouldn’t have failed the test.2.If you had followed my advice, you wouldn’t fail the test now.3.If you had studied hard before, you would have been a college student.4.If you had studied hard before, you would be a college student now.3.省略句1.If I were at school again, I would study hard=Were I at school again, I would study hard.2.If I had come earlier, you would have met me.=had I come earlier, you would have met me.3.If it should rain tomorrow, we wouldn’t go climbing=should it rain, we wouldn’t go climbing.4.名词性从句A.宾语从句1.Wish/would ratherA.I wish I could fly.B.I wish I had been there yesterday.C.I wish I were a bird.D. I would rather you hadn’t seen me before.E. Ｉwould rather you didn’t knew the news.2.order. Command, demand, request, require, desire, advise,A. The capital ordered that the crowds should protect the safety of passengers.B.My mother demand that I take the teacher’s advice.C. He advised that Tom not go out .D. He requested that students be sent to school before 7.E. The king commanded that he leave without anything.3.suggest和insist用法1.Tom suggested that we set off earlier.2.His red face suggested that he was annoyed.3.Tom insisted that the boy go with him.4. Tom insisted that he didn’t lie.主语从句1.It is desired that we get on well with other countries.2.It is strange that he have acted towards his parents like that.表语从句和同位语从句1.My idea is that we think it over again before accepting them.2.we all agree to his suggestion that we go to Dalian for sightseeing.3.My suggestion that he not go right now has been accepted by them.定语从句1.it is high time that you went to school. It is high time that you should go to school.方式状语从句和表语从句as if/as though1.He looks as if he were the artist.2. He speaks English so fluently as if he had studied English in America.3.He learns English so hard as if he would go to USA.4.If only I knew the answers.5.If only I had seen the film yesterday.介词with,without,but for, but that1.What would you do with 1,000,000 dollars?2.Without your help, we couldn’t have finish it ahead of time.3.But for your cooperation, we wouldn’t have done the work so well.4.But that he was afraid, he might have said no.含蓄条件句otherwise, or, but1. I was ill yesterday, or, I had been your party.2.I telephoned Tom yesterday, otherwise I would have known nothing about that.3.Ｉ should have given you more help, but i was too busy .4.I would be so glad to help you, but I am too busy now.5. I would have come to the party, but I was working.专项练习（）1.It is strange that the boy ______speak two languages.A.couldB.wouldC.shouldD.can（）2.he gave orders that the experiment ________before 5:30p.m.A.be finishedB.must be finishedC.will be finished（）3.he ________you more help, even if he was so busy.A.might have givenB.might giveC.may give（）4.Without the leadership of the party, there ______no New China.A.has beenB.wasC.should beD.would be（）5.He is talking so much about America as if he ________there.A.has beenB.had beenC.wasD.has gone（）6.The young man insisted that he _______nothing wrong and ______free.A.did, setB.had done, should be setC.should do ,setD.had done, must be set（）7.had you listened to the doctor, you _______right now.A.wereB.would beC.are（）8.You ________come a little earlier, the bus left a moment ago.A.wouldB.mayC.haveD.should have（）9.The ______look on her face suggested that she ____her manager’s idea.A.confusing,wouldn’t quite understand.B.confused,hadn’t quite understoodC.confusing,hadn’t quite understoodD.confused,shouldn’t quite understand （）10. A:Did Jack take the doctor’s advice that he ____in bed for a couple of days?B:If only he ______.A.lies,doesy,didC.lie,didD.lie,had（）11.A: Sorry for having kept you waiting.But for the traffic jam, I ___20 minutes earlier.B:Never mind. I haven’t been waiting that long.A.arrivedB.would arriveC.would have arrivedD.had arrived（）12.A:How much of the foreign expert’s speech have you understood?B: Next to nothing. I wish I _______harder at English.A.workedB.had workedC.would workD.were working（）13._______this afternoon, you would have to come again next week.A. The boss were not to returnB. The boss didn’t returnC.Didn’t the boss returnD.Were the boss not to return（）14._________for the fact that she got hit by a car and broke her leg on her way to school,she might have passed the exam.?A.Had it not beenB. Hadn’t it beenC.Was it notD.Were it not（）15.I din’t know your mobile phone number, otherwise I _____you the moment I got to Changsha.A.had rungB.would ringC.should have rungD.would have rung （）16.____it _____ to rain tomorrow, the sports meeting would be put off until the same time next week.A./should,/B.If,shouldC.Were, /D.If, were going（）17.A: Why didn’t you buy the gold ring yesterday?B:I _____,but I didn’t have the money.A.woud haveB.boughtC.would like toD.had bought。
专题2 情态动词和虚拟语气一．情态动词1.根据时间确定时态、时间段即要分清情态动词表推测时涉及的是现在情况还是过去情况。
原则上说，若对现在情况进行推测，情态动词后接动词原形或进行式；若对过去情况进行推测，则后接动词的完成式(这通常是高考的重点)；2.充分利用句子语境、语义综观历年考查情况，有相当一部分考题从本质上看都是在考查情态动词在具体语境、语义中的运用，即只要考生能弄清各个被考查情态动词的意思，就可作出正确选择。
3.注意分清适用句型即要分清所考查的情态动词是用于肯定句型，还是用于疑问句型或否定句型，同时还要注意情态动词在某些特殊情况下所使用的特殊句型。
4.掌握固定句式，从固定句式着手，套用句型。
题组训练（一）1.—Catherine, I have cleaned the room for you.—Thanks. You _________it. I could manage it myself.A. needn’t doB. needn’t have doneC. mustn’t doD. shouldn’t have done2. This cake is very sweet. You _________ a lot of sugar in it.A. should putB. could have putC. might putD. must have put3. —The woman biologist stayed in Africa studying wild animals for 13 years before she returned. — Oh, dear! She _________ a lot of difficulties!A. may go throughB. might go throughC. ought to have gone throughD. must have gone through4. Helen _________ go on the trip with us, but she isn’t quite sure yet.A. shallB. mustC. mayD. can5. —Do you know where David is? I couldn’t find him anywhere.—Well. He _________have gone far—his coat’s still here.A. shouldn’tB. mustn’tC. can’tD. wouldn’t6. He paid for a seat, when he _________ have entered free.A. couldB. wouldC. mustD. need7. —Lucy doesn’t mind lending you her dictionary.—She _________. I’ve already borrowed one.A. can’tB. mustn’tC. needn’tD. shouldn’t8. Zhang Lin was addicted to computer games during his last year in high school , otherwise he____________a student of Beijing University .A．would have been B．should be C．has been D．had been9. ---Your sister nearly _______ all her spare time to her study during the three years.----That's right，or she ________ the first place in her school in the College Entrance Examination.A. devoted; wouldn't have takenB. spent; wouldn't have takenC. had devoted; hadn't takenD. had spent; couldn't take10.—Any information about your son?—No. If only I ______ those tough words to him.A．didn't say B．hadn't saidC．shouldn't have said D．couldn't have said11. It is important that we _____ act out at once to protect the environment.A. wouldB. shouldC. willD. can12. John’s pale face suggested that he ______ill, and his parents suggested that he ______a medical examination.A. be, should haveB. was, haveC. should be, hadD. was, has13. But for the leadership of our Party and our Government, we __________ these splendid results. A．have achieved B．shouldn’t have achievedC．should have achieved D．would achieve14.He hesitated for a moment before kicking the ball, otherwise he ____ a goal.A. had scoredB. scoredC. would scoreD. would have scored【学法导航】考生在复习虚拟语气时要注意如下几点：1.把握虚拟语气的常用句式；2.正确辨析混合时间的虚拟语气，如果条件句中的动作和主句的动作不是同时发生，主句和从句的谓语动词的形式应分别根据各自所表示的时间加以调整。
三年级英语虚拟语气练习题40题(带答案)1.If I were a bird, I ____ fly high in the sky.A.canB.couldC.willD.would答案解析：D。
“If I were a bird”是虚拟语气，表示假设，对现在的假设主句要用“would+动词原形”。
A 选项can 不能用于虚拟语气；B 选项could 单独用不是虚拟语气中正确的形式；C 选项will 不能用于此虚拟语气。
2.If she had a magic wand, she ____ make all her dreams come true.A.canB.couldC.willD.would答案解析：D。
这是对现在的假设，虚拟语气中主句用“would+动词原形”。
A 选项can 不是虚拟语气的正确形式；B 选项could 单独用不对；C 选项will 也不正确。
3.If he ____ a superhero, he save the world.A.isB.wasC.were答案解析：C。
虚拟语气中，对现在的假设be 动词要用were。
A 选项is 和D 选项will be 都不是虚拟语气的形式；B 选项was 一般过去时，不符合虚拟语气要求。
4.If we had wings, we ____ travel anywhere easily.A.canB.couldC.willD.would答案解析：D。
对现在的假设，主句用“would+动词原形”。
A 选项can 不对；B 选项could 单独用不行；C 选项will 错误。
5.If they ____ fairies, they do magic tricks.A.areB.wereC.isD.will be答案解析：B。
虚拟语气，对现在的假设be 动词用were。
A 选项are 和C 选项is 都不是虚拟语气形式；D 选项will be 也不对。
情态动词表示说话人的语气和情绪，本身词义不全，不能单独作谓语，后面必须与动词原形一起构成谓语。
情态动词没有人称和数的变化，有的情态动词有过去式。
常见的情态动词有can, could, may, might, must, have to, shall, should, will, would, ought to, need, dare等。
（一）can和could1.表示体力或脑力(知识、技能)所产生的能力。
He could read books in English when he was only five.他只有五岁的时候就会读英文书籍了。
2.表示客观的可能性Anybody can make mistakes.任何一个人都有可能犯错误。
3.表示请求建议，用could 比 can语气更委婉 (回答用原形)Could you be here at eight o’clock tomorrow morning?你可不可以明天上午8点钟来这儿呢？4.表示允许、许可，用could 比 can更委婉客气。
Could/Can I borrow your reference books?我可以借用一下你的参考书吗？1.否定句、疑问句和感叹句中，表示怀疑、惊异、不相信的态度。
Can it be true? 难道这是真的？You can't be serious! 你怕不是在开玩笑吧！Oh, dear, what on earth can this mean? 哎呀，亲爱的，这究竟是意味着什么？2.表示“经过努力后终于能……”用be able toThe fire spread the building quickly but everybody was able to escape.大火迅速蔓延到整幢大楼，但大家都逃了出来。
注意：be able to比can有更多的形式变化When he grows up, he will be able to support his family.他长大后就能养家了。
人教版三年级英语虚拟语气练习题40题含答案解析1.If I were a bird, I ______ fly in the sky.A.wouldB.willC.shallD.can答案解析：A。
本题考查虚拟语气中对现在情况的假设。
if 引导的虚拟条件句中，be 动词用were，主句用“would+动词原形”。
选项B、C、D 都不是虚拟语气的正确表达形式。
2.If he ______ taller, he could play basketball better.A.wereB.isC.wasD.be答案解析：A。
对现在情况的虚拟假设，be 动词用were，主句用“would/could/should/might+动词原形”。
选项B、C、D 不符合虚拟语气要求。
3.If I had a magic wand, I ______ make all my dreams come true.A.wouldB.willC.shallD.can答案解析：A。
这是对现在情况的虚拟假设，主句用“would+动词原形”。
选项B、C、D 错误。
4.If she ______ more time, she would read more books.A.haveB.hasC.hadD.having答案解析：C。
对现在情况的虚拟假设，if 从句用过去式，主句用“would+动词原形”。
选项A、B、D 不正确。
5.If we ______ a car, we could travel around easily.A.haveB.hasC.hadD.having答案解析：C。
对现在情况的虚拟假设，if 从句用过去式，主句用“would+动词原形”。
选项A、B、D 错误。
6.If it ______ sunny tomorrow, we will go to the park.A.isB.wasC.wereD.be答案解析：A。
人教版三年级英语虚拟语气练习题40题含答案解析1.If I had a magic wand, I ______ make all my wishes come true.A.wouldB.willC.shallD.can答案解析：A。
本题考查虚拟语气的基本用法。
在虚拟语气中，如果表示与现在事实相反的假设，主句用“would+动词原形”。
选项B“will”和选项C“shall”一般用于一般将来时，不是虚拟语气的用法。
选项D“can”表示能力，也不符合虚拟语气的用法。
2.If I were a bird, I ______ fly freely in the sky.A.wouldB.willC.shallD.can答案解析：A。
如果表示与现在事实相反的假设，主句用“would+动词原形”。
选项B“will”和选项C“shall”不是虚拟语气的用法。
选项D“can”表示能力，不是虚拟语气的用法。
3.If I had more time, I ______ read more books.A.wouldB.willC.shall答案解析：A。
与现在事实相反的假设，主句用“would+动词原形”。
选项B“will”和选项C“shall”不是虚拟语气的用法。
选项D“can”表示能力，不是虚拟语气的用法。
4.If I were a superhero, I ______ save the world.A.wouldB.willC.shallD.can答案解析：A。
与现在事实相反的假设，主句用“would+动词原形”。
选项B“will”和选项C“shall”不是虚拟语气的用法。
选项D“can”表示能力，不是虚拟语气的用法。
5.If I had a car, I ______ go on a long trip.A.wouldB.willC.shallD.can答案解析：A。
与现在事实相反的假设，主句用“would+动词原形”。
虚拟语气Ｉ概念。
虚拟语气是动词的一种特殊形式，用来表达说话人的愿望，意图，建议，惊奇，设想等未能实现的情况，以及在说话人看来实现可能性很小的情况。
II.虚拟语气的特点：１．虚拟语气表达的是与客观现实相反的观念。
２．虚拟语气常由一个表示条件的从句和一个主句构成。
３．由于虚拟语气中条件从句中的条件是与客观事实相反，因此其主句的结论也只能是想象的，非真实的。
４．虚拟语气的特点决定了它句中动词形式的使用与真实句中的动词形式的是不同的。
同时，虚拟语气受时间的制约，分成以下三种句式：1）与_______事实相反的虚拟语气。
2）与_______事实相反的虚拟语气3）与_______事实相反的虚拟语气III.III.在不同时间下，虚拟语气的三种形式，公注：１。
虚拟语气中助动词be一律用________，不用was。
２．在与将来事实相反的虚拟语气中，“if＋主语＋should +Ｖ+…表示可能的假设1.与现在事实相反１）１）If I had a car, I should be very happy.= I should be very happy if I had a car, but ____________. 2)If I were a bird, I could fly.= I could fly if I were a bird, but I am not a bird, so I can’t fly.3)I he to ok his teacher’s advice, he might pass the exam.= He might pass the exam if he took his teacher’s advice, but hedoes n’t take his teacher’s advice, so he doesn't pass the exam. 4)If it were n’t raining, we should go for a picnic.= _______________________________________________.题例：1)1)If my father __________ here now, he _________ tell mewhat to do.A.A.were, would B were, will C is, would D is , will2)2)If I ________ a bee, I __________ work much harder.A were, wouldB were, shallC had, willD have,should3)3)If I _______ much money, I _________ buy a house.A have, willB had, shouldC had, willD have,should4)4)He __________ learn more quickly if he _________ harder.A will, workB would, workedC would, workD will , worked5)5)If I __________ you, I _________ do that.A was, wouldn’tB were, wouldn’tC am , won’t Dwere, won’t2.与过去事实相反例：1) If I had known her telephone number, I would have called her.= I would have called her if I had known her telephone number, but I didn't know hertelephone number, so I didn’t call her.2) If you had come ten minutes earlier, you could have metthat famous film star.= You could have met that famous film star if you had come ten minutes earlier, but________________________________________________________ ______________________________________3) If I had realized the importance of English study, I shouldhave worked much harder.= I should have worked much harder if I had realized the importance of English study, but_______________________________________________________ 题例：1)1)If you _________ the doctor’s advice, you would haverecognized already.A. followed B would follow C follow D hadfollowed2)2)If my lawyer __________ here last Saturday, he___________ me from going.A had been , would have preventedB had been, wouldpreventC were, would preventD were, would have prevented3)3)I __________ if she _________ me.A would have oversl ept , didn’t callB would haveoverslept, hadn’t calledC overslept, hadn't calledD would overslept, didn’t call4)4)---- If he ________, he ________that food.-----Luckily he was sent to the hospital immediately.A was warned, would not takeB had been warned, wouldnot have takenC would be warned, had not takenD would have beenwarned, had not taken5)5)She _______ to the party if she _______ invited.A would have gone, had beenB would go , wasC would have gone, wasD has gone3.与将来事实相反例：1）If I were to be twenty years old, I would take the course of computer science.= I would take the course of computer science if I were to be twenty years old, but I am not twenty years old, so I will not take the course of computer science.2) If I did /should do/were to do that , she would feel very surprised.= She would feel very surprised if I did/should do/were to do that, but I don’t do that, soshe will not feel surprised.3) If I failed, I would try again.= ______________________________________________题例：1)1)It’s quite impossible that it will rain tomorrow. But if it_________, I would still go to the park.A should rainB would rainC rainedD had rained2)2)I don’t think that I shall fail. But if I _______, I would try again.A should failB would failC failedD had failed3)3)________ tomorrow, what should we do?A If it rains B. Should it rain C. Would it rain D. Were itraining注：书面语中，“if”虚拟语气倒装形式的使用：如果“if”从句中含有“were, had ”或“should ”时，则可省略连词“if ”，而把“were, had ” 或“should” 移至主语之前。
例：1) Were I you (=I were you ), I would ….2) Had they not come last time (=I____________________),we would have done….3) Should it rain tomorrow (= ______________________),she would …注: 1.某些动词后宾语从句中的虚拟语气。
1.1.在动词suggest, insist, order, command, require, request ,demand 等后面的宾语从句中，动词形式一般用“should + 动词原形，或省略should用动词原形，用以表示一种建议，劝说，命令，要求的语气。
例：１）The teacher suggested we (should )finish that task at the end of next week.2)The officer ordered that the enemy (should ) besurrounded in the village before daylight.3)His uncle insists that he (should ) go to the most well-known university instead of some common ones.注意：1) 在It’s suggested /ordered/required/demanded/decided/necessary/important等结构的主语从句中，或suggestion, order, idea等词的同位语从句和表语从句中，也应用should +动词原形，或省略should ，以适合于说话人所表示的建议或要求，命令的语气。
