1、 can,could,may,might都可以用来都可以用来表示请求或给予许可。但用法上有表示请求或给予许可。但用法上有一些区别一些区别：1.can与与could can常用于口语中，表示非正式的请求，请求对象一般是家人或朋友。如：a)Can I borrow your bike,Simon?西蒙，我可以借一下你的自行车吗？Of course.当然可以。b)Can I have some milk,Mum?妈妈，我可以喝点牛奶吗？Yes,you can.好的。could是can的过去式，在口语中，could常用来代替can向对方更委婉地提出请求，用法上比can正式，可以用于向老师或长辈提出请求
2、，这时could不表示过去，回答一般还是用can。如：a)Could I use your computer,please?请问，我可以用一下你的电脑吗？Yes,you can.可以。b)Could I hand in our homework later,Mr Lin?林老师，我可以稍后交作业吗？No,you cant.不，不行。2.may与与might may也可以用来征求对方意见，意为“可以”，相当于could，用法也比can更正式，更礼貌，一般用于向陌生人或所尊敬的人请求许可。如：a)May I ask you a question?我可以问你一个问题吗？Yes,please.可以，请
3、问。b)May I come in,Mr Wu?吴老师，我可以进来吗？No,you may not.不行。might是may的过去式，它也可以用来表示征求对方意见，不过很少用。might在语气上比may更婉转，但不如may表现得那么自信，这时might不表示过去时态，肯定回答时通常用may。如：a)Might I join you?我可以加入你们吗？Yes,you may.可以。b)Might I have a look at your new plan?我可以看一下你的新计划吗？No,you may not.不，不行。Exercises:1.May I go surfing alone th
4、is afternoon,Dad?No,you _.It is dangerous.A.may not B.cant C.neednt D.dont 1.选B。这里是情态动词may 的否定回答。2.Can I get you a drink?_.I have already got one.A.Thats very nice of you.B.No,you dont have to.C.Yes,please.D.With pleasure.2.选B。这里can I 句子是征求意见，所以排除A、D。再根据下句I have already got one.说明“不需要”,故可排除C。3.Lin L
5、ings mother wanted to know _.A.if she studied hard at school B.how did she study at school C.what did she study at school 3.选A。此处为宾语从句，且从句的语序应为陈述句语序。4.Do you want to know _in the future?A special mirror invented by the French scientists can help you.A.what you will look like B.what will you look lik
6、e C.how do you look like D.how you look like 4.选 A。这里是宾语从句，应该用陈述句语序，排除B,C；“看上去怎样”疑问词应该用what，作为介词like 的宾语，排除D。5.It is said that the gravity on Mars is only about _ of the gravity on Earth.A.three-eighths B.third-eight C.three-eights D.third-eight 5.选A。这里考查的是分数的表达。that不能省略的几种情况不能省略的几种情况 在由that引导的宾语从句中
7、，由于连词that只起引导功能，无具体意义，不担当任何成份，因此在口语或非正式的文体中常可省略。然而，大凡规则总有例外的情况，在下列that引导的宾语从句中，that则不能省略。1.从句的主语是从句的主语是that。如：。如：He says that that is a real kings hat.他说那是一个真的王冠。2.that从句中含有主从复合句。如：从句中含有主从复合句。如：Im afraid that if youve lost it,you must pay for it.3.主从句之间有插入语时。如：主从句之间有插入语时。如：It says here,on this card,
8、that it was used in plays.卡片上写着，它是古代演戏用的。4.若出现两个或两上以上的由若出现两个或两上以上的由that引导的宾语引导的宾语从句，且由并列连词连接时，只有第一个从句，且由并列连词连接时，只有第一个连词连词that可以省略。可以省略。如：She said(that)she would come and that she would also bring her son.她说她要来，还要带她的儿子来。if，whether引导的宾语从句引导的宾语从句.if和和whether引导宾语从句时，作引导宾语从句时，作“是否是否”讲，一般情况下，二者没有区别，可以换用。讲
9、，一般情况下，二者没有区别，可以换用。但但if常用于口语中，常用于口语中，whether比较正式。比较正式。如：Millie asked if/whether he liked this sweater.米莉问他是否喜欢这件羊毛衫。The fisherman wants to know if/whether it will rain.渔民想知道天是否会下雨。.if和和whether引导宾语从句时，要注意宾引导宾语从句时，要注意宾语从句三要素，即连词、语序和时态。由语从句三要素，即连词、语序和时态。由于于if和和whether连接的是一般疑问句，因此连接的是一般疑问句，因此要注意把从句语序改为陈
10、述句语序。要注意把从句语序改为陈述句语序。如：Does Mr Zhao live in Room 208?Could you tell me?Could you tell me if/whether Mr Zhao lives in Room 208?其次要注意时态变化：1.若主句是一般现在时，从句用任何所需时态。若主句是一般现在时，从句用任何所需时态。如：He wants to know if/whether they had a good journey home.他想知道他们回家旅途是否愉快。2.若主句是一般过去时，从句则用跟过去相关的时若主句是一般过去时，从句则用跟过去相关的时态。即一
11、般现在时变为一般过去时、现在进行时态。即一般现在时变为一般过去时、现在进行时变为过去进行时、一般将来时为过去将来时、现变为过去进行时、一般将来时为过去将来时、现在完成时态变为过去完成时。在完成时态变为过去完成时。如：Did the train leave?She didnt know.She didnt know if/whether the train had left.if和和whether的区别。的区别。二者在下列几种情况下不能换用：1.宾语从句置于句首表示强调时，应用宾语从句置于句首表示强调时，应用whether，不用，不用if。如：Whether this is true or no
12、t,I cant say.这是否对，我不能说。2.宾语从句与宾语从句与or not直接连用时，应用直接连用时，应用whether，不能用不能用if。如：I dont know whether or not he will come tomorrow.我不知道他明天是否要来。3.与动词不定式连用时，只能用与动词不定式连用时，只能用whether。如：She cant decide whether to go to America.她不能决定是否去美国。4.从句作介词宾语时，只能用从句作介词宾语时，只能用whether。如：I worry about whether I hurt her feel
13、ing.我担心是否伤了她的感情。5.宾语从句的谓语动词是否定形式时，只能用宾语从句的谓语动词是否定形式时，只能用if，不能用，不能用whether。如：Tom wants know if he wont come here tomorrow.汤姆想知道他明天是否不来这儿。6.if意为意为“假如，如果假如，如果”时，可以引导条件状时，可以引导条件状语从句，而语从句，而whether没有这个用法。没有这个用法。如：If Simon comes here tomorrow,Ill call you.假如西蒙明天来这儿，我将打电话告诉你。选择填空。选择填空。1.I dont know if Mr.Wa
14、ng _on a field trip.If he _ on a field trip tomorrow,please call me.A.goes;will go B.will go;goes C.will go;will go D.goes;goes 2.She asked me if I knew _.A.whose pen was it B.whose pen it was C.whose pen it is D.whose pen is itExercises:3.They wondered if the teacher _ us English the next term.A.wo
15、uld teach B.had taught C.will teach D.taught4.The boy asked _ any noise from outside.A.whether had I heard B.whether I had heard C.whether have I heard D.whether I have heard5.I havent decide _ Ill go out or stay at home.A.if B.when C.why D.whether6.I want to know _ he loves you.A.that B.what C.if D
16、.who7.I wondered _ our teacher was going to attend our party.A.whether B.why C.where D.that8.Id like to know _ or not.A.whether will he come B.whether has he come C.whether he will come D.that he will come根据汉语提示，用英语完成句子。根据汉语提示，用英语完成句子。1.我们不知道我们能否在火星上种植植物。We are wondering _ on Mars.2.你能告诉我是不是有许多人打算搬到
17、火星上去吗？Could you tell me _ to Mars?whether/if we can grow plantsif/whether many people are going to move3.我不知道他在家洗不洗衣服。I dont know _ any washing.4.我担心是否伤害了她的感情。I was worried about _.whether or not he doeswhether I hurt her feelings1.Uncle Wang came up to see _there was anything wrong with the machine.2.The shop keeper asked my father _ or not he wanted to choose a big Christmas tree.用用if/whether填空。填空。if/whetherwhether3.I dont know _ to go or stay?4._ that is true,what should we do?whetherIf5._ they will ever become future Olympic champions,only time will tell.Whether
