八年级下册语法知识重点八年级下册语法知识重点八年级下册语法知识重点1.If 引导的条件状语从句（1）当主句和从句所表示的是原理、客观事实、规则时，主句是一般现在时（包括祈使句和含有情态动词can，may，must等），从句也用一般现在时。

e.g.1.You must see the doctor if you are ill.如果你生病了，你就必须去看医生。

（含情态动词）2.If you stick a pin into a balloon , it bursts.如果你用针刺气球，它就会爆炸。

（原理）3.Be careful if you cross the road.如果你过马路，请小心。

（祈使句）（2）在if引导的条件状语从句中，如果从句谈论的时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。

e.g.1.If it rains tomorrow, we will not go to the zoo.2.If you go to bed earlier, you won’t feel tired in the morning. 2.后带ing和do的动词3.情态动词Should一、作为情态动词，通常用来表示现在或将来的责任或义务，表示“应该，应当”。

e.g.Crime should be punished. 犯罪应受惩罚。

二、作为情态动词，可以用来表示有较大可能实现的猜测、推论，表示“可能，该(=will probably) ”。

e.g. The headmaster should arrive soon. 校长可能很快就到了。

They should be home by now，I think. 我想现在他们总该到家了吧。

Exercise: 情态动词练习题1. Jean ___have kept his promise.I wonder why he changed his idea.A.mustB.shouldC. needD.would2.---Could I use your bike?----Yes,surely you___.A.mightB.willC.canD.should3.It’s nearly eight o’ clock.Bruce___be here at any momentA.mustB.needC.shouldD.can4.Tommy,you___play with the knife,you___get hurt.A.won’t; can’tB.mustn’t; mayC.shouldn’t; mustD.can’t; shouldn’t5.When he was there,he___go to that coffee shop at the corner after work every day.A.wouldB.shouldC.had betterD.might6.---When can you get the film developed?I need it tomorrow morning. ----It ___be ready by 8：00.A.canB. shouldC.mightD.need7.---Will you stay for another hour?-----Sorry,___.One of my best friends is coming to see me.A.I mustn’tB.I can’tC.I needn’tD.I won’t8.Jason shouldn’t___me your secret,but he meant no harm.A.have toldB.tellC.be tellingD.having told9.---Are you coming for dinner?----I’m not quite sure.I___go to my uncle’s instead.A.mustB.wouldC.shouldD.might10.---Don’t forget to visit me when you come to Beijing.------___.A.I don’tB.I won’tC.I can’tD.I haven’t11.He ought___have done so even though possible.A.not toB.to notC.notD.never12.Jane___have come to the party,but she ___not find the exact time.A.could;couldB.might;couldC.should;couldD.should;would13.So many mistakes in your homework!You___more careful.A.may beB.had toC.would beD.should have been14.Her brother___be at home now,because he was seen playing basketball in the stadium just now.A.mustn’tB.needn’tC.can’tD.shouldn’t15.---I can’t understand why our boss is late.------He___the early bus.A.could missB.may have missedC.can have missedD.might miss 答案：1---5 BCCBA 6---10 BBADB 11---15 AADCB4.动词+介词/动词+副词动词+介词：构成的词组相当于一个及物动词，宾语总是在介词后面。

e.g.I don’t much care for the television. 我不是很喜欢电视。

动词+副词：构成的词组可作及物动词，也可作不及物动词。

作及物动词时，宾语的位置有两种情况：宾语如果是名词，则可放在副词后面，也可放在动词与副词之间；而如果宾主是代词，只能放在动词后面，即动词和副词之间。

作不及物动词时，后不带任何名词或代词作宾语。

e.g.Something unexpected has turned up.出现了令人意外的情况。

5.后带to do（动词不定式）的动词6.Have to 与mustHave to 表示“不得不”，强调客观需要，有人称、时态和数的变化；而must则着重说明主观看法，表示个人的意志，是情态动词，没有人称、时态和数的变化。

E.g.Did she have to pay a fine? 她非得交罚款吗？I must go there to help the poor.我必须去那儿帮助那些穷人们。

（表示说话人自己的看法）在某些不需要强调这两种差别的场合，两者可以互换。

e.g.I am afraid we have to / must leave now. 恐怕我们必须得走了。

Summary7.词语辨析1 pay, spend, take, cost2 sometimes，some times，sometime与some time3how often，how long，how soon 与 how many timese.g.1.How do you exercise?2.How does it take to get to Shanghai from here?3.How is the river?4.How is it from here to the park?5.How have you been here?8.状语从句在句中作状语的从句，分为九种，常见的有时间状语从句，原因状语从句，条件状语从句，结果状语从句及目的状语从句。

1Until引导的时间状语从句Until意为“直到……，在……之前”。

Until 和not...until的区别e.g.Continue in this direction until you see a sign. 一直朝着这个方向走，直到你看见一个指示牌。

I didn’t wake up until I heard the alarm clock. 直到听到闹钟响我才醒来。

Summary:2so that引导的目的状语从句So that是连词，意为“为的是，以便”。

注意so that, in order that 和in order to的区别。

So that/in order that后加从句，而in order to 后加短语。

3unless引导的条件状语从句Unless是“除非，如果不”，相当于if...not。

e.g.I won’t go to the party unless I’m invited. 除非我被邀请，否则我不会去参加晚会的。

4as soon as引导的时间状语从句意为“一……就……”。

e.g.He will report back here as soon as he arrives. 他一到达就会来这里汇报的。

5so...that/such...that引导的结果状语从句句型中so是副词，常用来修饰形容词或副词，意思是“如此……以至于”，常用句型为：主语+谓语+so+adj./adv/+that从句。

Such...that句型中such是形容词，修饰名词，意思是“如此……以至于”，常用句型为：A.主语+谓语+such+adj.+复数可数名词+that从句；B.主语+谓语+such+a(an)+adj.+单数可数名词+that从句；C.主语+谓语+such+adj.+不可数名词+that从句。

由so...that引导的从句可转换成含不定式的简单句，即可转换为”...enough to...”或”too...to...”。

He was so clever that he could understand what I said.→He was clever enough to understand what I said.The question is so easy that I can work it out.→The question is easy enough for me to work out.The bag is so heavy that she can’t move it.→The bag is too heavy for her to move.The girl is so young so that she can’t dress herself.→The girl is too young to dress herself.9.过去进行时与when/while引导的时间状语从句When 当……的时候while 在……期间before 在……之前After 在……之后 as 当……的时候 since 自从Until 直到……10.感叹句11.询问某国/地区“多少人口”时，问程度用“How large...”；问数量用“What...”表示人口“多”或“少“时，用big/large或small修饰population；population作主语时，谓语动词一般用单数形式；表达某一地区或某一个国家”有多少人口“时，可用下列句型：A.“地区/国家”+has a population of+具体数词；B.The population of +“地区/国家”+is +具体数词。