高中英语语法
一、表语从句
1.定义：用作表语的从句叫做表语从句。
2.构成：关联词+简单句
3.引导表语从句的关联词的种类：
(1)从属连词that。如：The trouble is that I have lost his address.麻烦是我把他的地址丢了。
(2)从属连词whether,as,as if。如：He looked just as he had looked ten years before.他看起来还与十年前一样。
注：从属连词if一般不用来引导表语从句，但as if却可引导表语从句，如：All this was over twenty years ago,but it's as if it was only yesterday.这都是20多年前的事了，但宛如昨天一样。能跟表语从句的谓语动词一般为系动词be,seem,look等。
(3)连接代词who,whom,whose,what,which,whoever,whatever,whichever 连接副词 where,when,how,why。如：The problem is who we can get to replace her.问题是我们能找到谁去替换她呢。
解释：连词because可引导表语从句。如：I think it is because you are doing too much.我想这是因为你做得太多。在一些表示“建议、劝说、命令”的名词后面的表语从句中，谓语动词用虚拟语气。should+动词原形表示，should可省略。如：My suggestion is that we (should)start early tomorrow.我的.建议是我们明天一早就出发。
二、主语从句
1.定义：用作主语的从句叫做主语从句。
2.构成：关联词+简单句
3.引导主语从句的关联词有三类：
(1)从属连词that。如：That they were in truth sisters was clear from the facial resemblance between them.很明显，她们确是亲姐妹，她们的脸型很相似。
(2)从属连词whether。如：Whether he’ll come here isn’t clear.他是否会来这里还不清楚。
(3)连接代词who,whom,whose,what,which,whoever,whatever,whichever 连接副词 where,when,how,why。如：What she did is not yet known.她干了什么尚不清楚。
三、宾语从句
1.定义：用作宾语的从句叫宾语从句。
2.构成：关联词+简单句
3.引导宾语从句的关联词有三类：
(1)从属连词that。如：He told us that he felt ill.他对我们说他感到不舒服。I know he has returned.我知道他已经回来了。注：that在引导宾语从句时也并不是任何情况下都可以省略。在以下情况下，that不能省略。
1.Everybody could see what happened and that Tom was frightened.(and连接两个宾语从句，that宾语从句放在and的后面时，that不能省略。)大家都会看出所发生的事情并知道Tom非常害怕。
2.I know nothing about him except that he is from the south.(that引导的宾语从句作介词宾语时，that不能省略。)对他我一无所知，只知道他是南方人。
3.That he ever said such a thing I simply don’t believe.(that从句位于句首时，that不可省略。)我简直不相信他曾说过这样的话。
4.We decided,in view of his special circumstances,that we would admit him for a probationary period.(主句谓语动词与that从句之间有插入语，that不可省略。)鉴于他的特殊情况，我们决定应允他一段试用期。
(1)介词宾语从句 宾语从句也可用作介词的宾语。如：He was deeply displeased by what had occurred that day.他对那天发生的事感到很不快。
(2)从属连词if/whether。如：I doubt whether he will succeed.我怀疑他是否会成功。I don’t know if you can help me.我不知道你能否帮助我。
(3)连接代词who,whom,whose,what,which,whoever,whatever,whichever 连接副词 where,when,how,why。如：Who or what he was,Martin never learned.他是什么人?他是干什么的?马丁根本不知道。
四、同位语从句
1.定义：用作同位语的从句叫做同位语从句。
2.用法：同位语从句的先行词多为fact,news,idea,thought,question,reply,report,remark等，关联词多用从属连词that。如：They were all very much worried over the fact that you were sick.对你生病这件事，他们都很焦虑。
注：同位语从句偶尔由从属连词whether引导。如：I have no idea whether he’ll come or not.我不知道他是否来。
连接代词who,which,what和连接副词where,when,why,how亦可引导同位语从句。
五、不定式的构成
不定式是由不定式符号to+动词原形构成，在某些情况下to也可省略。
不定式的一般式所表示的动作通常与主要谓语的动作同时或几乎同时发生，或是在它之后发生。如：They invited us to go there this summer.他们邀请我们今年夏天去那儿。