if条件状语从句及其时态的用法

if条件状语从句及其时态的用法条件状语从句及其时态的用法 英国前首相撒切尔夫人（Margaret Thatcher）曾用if条件句对男人和女人进行评价：In politics,if you want someone to make a speech,ask a man;if you want something done,ask a woman.一、概念一、概念 连词if的意思是“如果”，它引导的句子表示某事发生所需要的条件，即“在条件下某事才能发生”，在句子中充当状语，因此我们称之为条件状语从句。在复合句中连词if引导的句子为从句，被修饰的句子为主句。从句可以放在主句后，也可以放在主句前，从句放在主句前时，应用逗号将它与主句隔开。例如：Well go to the Great Wall if it doesnt rain tomorrow.=If it doesnt rain tomorrow,well go to the Great Wall.二、用法二、用法 1.条件状语从句通常由连词if引导，意为“如果，假如”，主句不能用be going to 表示将来，而应该用shall或will。例如：If Im free tomorrow,Ill go with you.2.if引导的条件状语从句，主句用一般将来时，从句则用一般现在时，即“主将从现主将从现主将从现主将从现”。例如：If it is sunny tomorrow,Ill climb the hill.3.正确区分if引导的条件状语从句和if引导的宾语从句：在条件状语从句中，if表示“如果”；而在宾语从句中，if表示“是否”。可以用下面的方法区分：1)从句前置法从句前置法：if引导的条件状语从句，可以放在主句之前并用逗号隔开，也可放在主句之后；而if引导的宾语从句只能放在主句之后。因此如果把if放在主句之前，句子通顺，意义不变，则是条件从句，否则是宾语从句。例如：He will help you if you ask him.=If you ask him,he will help you.2)whether替换法替换法：if引导宾语从句时，其意为“是否”，通常可用whether替换，意义不变，而if引导条件状语从句时不能用whether替换。因此，可用whether替换的是宾语从句，不能替换的是条件从句。例如：I want to know if you will go tomorrow.=I want to know whether you will go tomorrow.注意：注意：区分if的用法有着极为重要的意义，因为在条件状语从句中，主句用将来时，从句用一般现在时；而在宾语从句中，当主句是一般现在时，从句可用所需的任何时态，主句是一般过去时，从句用过去的某种时态。巩固练习巩固练习一、单项选择一、单项选择 1.If you _ to the party,youll have a great time.A.will go B.went C.go D.going 2.I _ her the answer if she _ me.A.can tell,will ask B.will tell,will ask C.would tell,ask D.will tell,asks 3.What are you going to do tomorrow?Well go to the library tomorrow if it _.A.isnt rain B.rain C.wont rain D.doesnt rain 4.Do you know when he will come back tomorrow?Sorry,I dont know.When he _ back,Ill tell you.A.comes B.will come C.come D.may come 5.Ill give the book to him if he _ here next Sunday.A.will come B.comes C.is coming D.came 6.There _ an English film in our school tomorrow.A.is going to have B.will have C.is going to be D.has 7.Ill wake you up when he _back.A.will B.is going to come C.comes D.come 8.The football match will be put off if it _.A.will rain B.rains C.rainedD.is rained 9.There _ a basketball game this afternoon.A.is going to haveB.will be C.is going to play D.will play 10.I wont go if it _ tomorrow.A.rain B.is raining C.rains D.will rain二、用所给词的适当形式填空二、用所给词的适当形式填空1.If you _(feel)tired,you _(have)to have a rest.2.Where _ he _(see)the film if he _(have)time?3.If there _(be)fewer trees,there _(be)more pollution.4.He _(dress)more casually if he _(not work)on weekends.5.If Marcia _(live)alone,she _(keep)a pet parrot.6.Lana _(buy)a new dress if the old one _(be)out of style.7.The twins _(fight)if they _(argue).8.I _(have)a bake sale if I _(need)money for education.9.Peter _(send)me a beautiful souvenir if he _(go)to Spain.10.If Mr.Green _(say)I am hard-working,my parents _(feel)glad.11.I _(go)to the beach if it _(not rain)this week.12._they _(have)a match if the P.E.teacher_(be)not busy?13.He _(write)a letter to his grandparents if he _(get)his report card this week.14.If she _(get)up late,she _(not catch)the early bus.15.Peter _(major)in English if he _(pass)the exams in Peking University.三、完成句子三、完成句子1.如果他迟到了，会发生什么事情？What _ _ if he _ late?2.如果努力学习，你就会取得好成绩。If you_ _,you _ _ good _.3.他如果看电视太久了，他的父母会不高兴。If he _ TV too much,his parents _ _ unhappy.4.如果我们为他举办生日聚会，大家都会来的。Everyone _ _ if we _a birthday party _ him.5.如果明天不下雨，我会和你一起去公园的。If it _ _ tomorrow,I _ go to the park _ you.6.如果她睡过头了，就会误了开会的。She _ _ _ _ the meeting if she _ _.7.如果他有空，他会帮助你的。If he _ _,he _ _ you.8.如果Tom考试不及格，他就没有机会上高中了。Tom _ miss the chance to go to the high school if he _ the exams.9.你如果抄同学的作业就不能学好各门功课。You _ _ good at all the subjects if you _ the other students homework.