①If I had wings， I could fly in the sky.
②If we had started a little earlier yesterday， we could have caught the train.
③If it should rain tomorrow， we would not go out.
④If you had followed the doctor’s advice， you might be all right now.
2.wish后的宾语从句或as if (though)引导的状语从句
与将来事实相反： 谓语用should， would， could或might+动词原形。例如：
①He wishes that I was a doctor.
②I wish that I had finished my homework yesterday.
③They wish that they would live on the moon someday.
④It seems as if it was spring already.
⑤They talked as though they had been friends for years.
3.在It is high(good， about) time或would rather后的从句中，动词常用过去式。例如：
①It is high time that we went to bed.
②I would rather you came tomorrow.
1.在某些表示请求﹑建议﹑命令﹑筹划等含义的动词suggest， insist， order， demand， command， propose， request， desire， arrange等后面的宾语从句，以及上述动词所对应的名词引起的主语从句﹑表语从句或同位语从句中， 谓语用should+动词原形， should常可省略。例如：
①He suggested that we (should) put on a play at the English evening.
②My idea is that we (should) put off the meeting.
③It was ordered that the guns (should) be sent to the front.
④He made the suggestion that they (should) speak English in the party.
①It is a pity that he (should) be so stupid.
②It is incredible that he (should) have finished his homework so soon.
3.在lest， for fear that， in case等引起的从句中，谓语用should+动词原形，should常可省略。例如：
①He took his umbrella with him in case he (should) be caught in the rain.
②She burned the letter for fear that it(should) fall into the enemy’s hands.
without， under， but for等)﹑连词(如： otherwise， or， but等)﹑不定式或分词等。
①But for their help， we could not have finished the task on time.
②Without water， there would be no life.
③It would be a mistake not to help her.
④I was busy that day. Otherwise I would have taken part in the party.
1.条件句中含有had， were， should， could等时，如果省略了if，就要把这些词提到句首构成倒装。例如：
①Had I known of your arrival， I would have met you at the airport.
②Were I in your position， I would accept their offer.
①The child would have been saved. (省略了If the doctor had been there.)
②If only I had attended the meeting. (省略了I would have put forward a proposal.)
1.They ____ you more help， but they were so busy that day.
A. had givenB. would give
C. gaveD. could have given
2. It is strange that he ____ to pass the exam.
A. has failedB. have failed C. failedD. would fail
3. The headmaster gave an order that the cleaning ____ before 5：00.
A. will be finished B. would be finished
C. were finished D. be finished
4. I was ill that day. Otherwise I ____ the party.
A. would attendB. would have attended
C. had attendedD. attended
5. If you had finished the work yesterday， you ____ busy now.
A. is notB. will not be
C. would not beD. would not have been
6. Tom insisted that he ____ the man break into the room.
A. should see B. see C. had seenD. have seen
7. We accepted the suggestion that ____ by Professor Smith in the
A. should be put forwardB. be put forward
C. was put forward D. would be put
8. Mary always obeyed her parents lest they ____ angry.A. wereB. had been C. wasD. be
9. He would rather ____ at home to watch TV play.
A. stayed B. stays C. stayD. had stayed
10. The expression on her face suggested that she ____ the exam.
A. pass B. should have passed
C. had passed D. have passed
11. The boy talks as if he ____ a doctor.
A. is B. were C. have been D. be
12. He wishes that he ____ the maths problem yesterday.
A. worked out B. works out
C. has worked outD. had worked out
13. It is about time that we ____ a rest.
A. will have B. can have C. had D. might have
14. It was the doctor’s advice that the patients ____ quiet.
A. be keptB. would be keptC. would keepD. kept
15. Look at the heavy clouds. It looks as if it ____.
A. was going to snow B. is going to snow
C. be going to snow D. snowed
Key：1.D 2.B 3.D 4.B 5.C 6.C 7.C 8.D 9.C 10.C 11.B 12.D 13.C14.A 15.B