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1、 由 if 和unless 引导的条件状语从句 1. If we lose our short-term memory, we forget things happening recently. 译：_ 2. If the picture is silly, strange and colorful, you will remember it better.译：_A: If sentences: actions with definite results. 有必然结果发生的行动 eg: If you go into a clothes shop, you find clothes. If yo
2、u go into a car showroom, you see cars. Water turns into ice if you cool it. The wood floats if you put it into water.Conclusion: 1). 如果 if 条件句谈论的是重复发生和预示必定要发生的情景和事件，则主从句大多用一般现在时态。 2). 在if 条件句中，if 条件从句可以放在前面，也可以放在后面。当if 引导的条件从句放在前面时，后面常用逗号隔开。B: If sentences: actions with possible results. 有可能性结果发生的行
3、动 eg: If you ask him，he will help you 如果你请他帮忙，他会帮你的。 If you fail in the exam，you will let him down 在 if 引导的条件状语从句中,如果从句谈论的是一个有可能发生的事实及其产生的相关的结果，主句用一般将来时态，从句用一般现在时态。 C: unless引导的条件状语从句：unless= if not. conj. 除非, 若不, 除非（否则） e.g.: Lets go out for a walk unless you are too tired.= If you are not too tied
4、, lets go out for a walk. 我们出去散步吧，除非是你太累。译：如果你不早点出发,你就不能及时赶到那儿。 我们可以把unless或ifnot 从句放在句子开头或末尾。You will be late for school unless you leave now. = Unless you leave now, you will be late for school. 除非你早点出发，（否则）你上学会迟到。You will be late for school if you dont leave now. =If you dont leave now, you will
5、be late for school. 如果你不早点出发，你上学迟到。 “if ” 引导的条件状语从句的用法,现在总结一下:1)引导条件状语从句最常用的连词是if。 if 引导的条件句有真实条件句和非真实条件句两种（非真实条件句会在以后的虚拟语气中阐述），其引导的真实条件状语从句表示在某种条件下某事很可能发生。2）if 条件句不一般,几个要点记心间; 条件句,放在前,逗号要放句中间。条件句表可能，主句多用将来时；条件句表事实，主句常用现在时。【巩固练习】一if和unless句型互改。Eg: You will fail the exam if you dont work hard. = You
6、will fail the exam unless you work hard.1）Unless you obey the rules, you will be punished. =_.2) A fish dies if you dont keep it in the water. =_3) No body can learn English well if he doesnt work hard on it. =_.4) Unless you start right now, you will be late for the meeting. =_.二用if 或unless 填空。1. y
7、ou put wood into water, it floats.2. I sleep with the window open it is really cold.3. You will not improve your skill in a short time _ you practice playing the violin regularly.4. Ice melts you heat it.5. you boil water, it becomes steam （蒸汽）.6. you dont work hard, you will fail the exam.7. He can
8、t be here on time he gets up early.8. you dont have enough sleep, you will feel tired.9. it is fine tomorrow, I will go fishing with my dad.10. you finish your homework, you will not go out to play.三单项选择。1. You will not remember the facts you understand them well.A. if B. unless C. if not D. because
9、2. Shenzhen a dirty place if we the ground.A. is; litter B. will be; will litterC. is; are litteringD. will be; litter3. If you harder, you will fail the exam.A. not work B. work C. dont work D. wont work4. you obey the rules, you will be punished.A. If B. Since C. Because D. Unless5. He cant see th
10、e words on the board unless he his glasses.A. wear B. wears C. doesnt wear D. to wear6. If you plant seeds in soil, .A. it grows B. they grow C. you grow D. it will grow7. If you check your timetable every night, it _ in your mind better.A. will stay B. stay C. stayed D. staying8. A tourist will eas
11、ily lose his way in Beijing _ he has a map or guide. A. ifB, becauseC. unlessD. when9. I shall telephone the police and complain about it _ _ the noise .A. if, stops B. unless, stopsC. if not, stops D. unless, stop10. I sleep with the window open its really cold.A. if B. if not C. unless D. until11.
12、 _ you try, you will never succeed. A. IfB. UntilC. SinceD. Unless12. _ he doesnt come on time, we will go without him. A. IfB. UnlessC. WhenD. Because13. I will come to see you if it _ rain tomorrow morning. A. wont B. didntC. doesntD. dont14. If you take a fish out of the water, it _. A. dieB. diesC. will dieD. has died15. -Shall Tony come and play computer games? -No, _ he has finished his homework. A. whenB. ifC. unlessD. once