1、单元语法小专题(Grammar Focus)语法精讲if引导的条件状语从句条件状语从句通常由连词if引导，意为“如果；假设；倘假设，表示在某种条件下，很可能会发生某种事情或不发生某种事情。1if条件状语从句的位置在 if 引导的条件状语从句中，if 条件句位置比拟灵活，可放在主句前面也可放在主句后面。假设放在主句前，从句后面要用逗号和主句隔开。如：If he doesnt feel tired，he will visit the museum.He will visit the museum if he doesnt feel tired.如果他不感觉累，他就去参观博物馆。2if条件状语从句的
2、时态搭配(1)当主句用一般将来时，if 引导的条件状语从句要用一般现在时。如：If it rains tomorrow，I wont climb the hills.如果明天下雨，我就不爬山。(2)当主句中含有can，may，must等情态动词时，if 引导的条件状语从句要用一般现在时。如：We can win the basketball game if he joins us.如果他参加我们，我们就能赢这场篮球赛。(3)当主句是祈使句时，if 引导的条件状语从句要用一般现在时。如：Help your mom with the housework if you finish your hom
3、ework early.如果你完成作业早，就帮你妈妈做家务。if条件状语从句用法歌诀：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。3与其他句式之间的转换(1)借助“祈使句 and/or 一般将来时的句子这一句型来转换。and在句意上表示顺承关系，or表示转折关系。如：If you get up early，youll get there on time. Get up early，and youll get there on time.Get up early，or you wont get there o
4、n time.早点起床，你就会准时到那里。(2)借助介词without或with来转换条件状语从句。如：If there is no water，fish will die.Fish will die without water.如果没有水，鱼就会死。If you help me，Ill finish the work soon.With your help，Ill finish the work soon.如果你帮助我，我就会快点完成工作。(3)if not引导的条件状语从句，可以借助连词unless来改写。如：You will be late if you dont go there by
5、 bus.You will be late unless you go there by bus.如果你不乘公共汽车你就会迟到。语法精练.用括号内所给单词的适当形式填空。1If it rains tomorrow，I _(stay) at home.2He will take a trip to Beijing if he _(be not) busy next week.3Please tell Li Jun about it if he _(come) back.4If you dont wear your school uniform to the party，the teachers
6、_(not let) you in.5She _(not go) shopping with her parents if it snows this afternoon.单项选择。( )6.Do you know when he will come back tomorrowSorry，I dont he _ back，Ill tell you.Acomes Bwill comeCcome Dmay come ( )7.Mary will go to Sanya if she _ a fiveday trip.Ahave BhadCwill have Dhas( )8.What will y
7、ou do if you _ to the party without invitationAgo Bwent Cgoing Dwill go ( )9.If I eat too much food，I _ too fat.Aam Bwas Cwill Dwill be( )10.Ill give the book to him if he _ here next Sunday.Awill come BcomesCis coming Dcame.同义句改写，每空一词。11Study hard，or you wont pass the exam.If you study hard，you _ _
8、 the exam.12Take a taxi，and youll catch the train._ you _ a taxi，youll catch the train.13If you dont help me，I cant catch up with the others.I cant catch up with the others _ _ _14We will be late for the meeting if we dont be quick.We will be late for the meeting _ _ _ _15If you are late，the teacher will be angry. _ _ late，_ the teacher will be angry.单元语法小专题(Grammar Focus) stay2.isnt4.wont let5.doesnt go.610ADADB pass；take your help we are quick15.Dont be；or
