高二英语Unit5语法知识是主语从句，主语从句指在复合句中充当主语成分的句子，在主句中不要求做何成分。
一、引导主语从句的连词主要有：
从属连词：that whether
连接代词：who whoever whom whose what whatever which whichever
连接副词：when where how why
二、用法
主语从句是在复合句中充当主语的从句，通常放在主句谓语动词之前或由形式主语it代替，而本身放在句子末尾。
1. It 作形式主语和it引导强调句的比较
①主语从句常用it作形式主语，一般常用句型为：It is+{名词/形容词/过去分词}+主语从句例如：
It is still a question whether she will come or not.
It is strange that you should like him.
It is still unknown which team will win the match.
另外，还有一些比较多见的结构：
It turned out that……;
It has been proved that……;
It happened/occurred that……;
It is well-known that……等等
②而强调句则不同，它的结构是：It+be+被强调部分+that+从句
强调主语：It is the times that produce their heroes.时势造英雄
强调宾语：It is English that Prof.Lin teaches us.
强调状语：It was in shanghai that I saw the film.
判断是否是强调句有一个方法，就是将that以后的“句子的其余部分”拿出来单独看，看有没有缺成分，缺的是什么成分，再把谓语动词后面that前面的那部分，带到你认为缺成分的地方，如果放进去是一句完整的句子了，那就说明是强调句。
2. 用it 作形式主语的结构
(1) It is +名词+that从句
It is a fact that … 事实是……
It is an honor that …非常荣幸
It is common knowledge that …是常识
(2) it is +形容词+that从句
It is natural that… 很自然……
It is strange that… 奇怪的是……
(3) it +不及物动词+that从句
It seems that… 似乎……
It happened that… 碰巧……
(4) it is+过去分词+that从句
It is reported that… 据报道……
It has been proved that… 已证实……
3.主语从句不可位于句首的五种情况
(1) if引导的主语从句不可居于复合句句首。
(2) It is said , (reported) …结构中的主语从句不可提前。例如：
It is said that President Jingo will visit our school next week.
(3) It happens…, It occurs… 结构中的主语从句不可提前。例如：
It occurred to him that he failed in the examination.
(4) It doesn’t matter how/whether …结构中的主语从句不可提前。例如：
It doesn’t matter whether he is wrong or not..
(5) 含主语从句的复合句是疑问句时，主语从句不可提前。例如：
Is it likely that it will rain in the evening?
4. What 与that 在引导主语从句时的区别
What 引导主语从句时在从句中充当句子成分，如主语.宾语.表语，而that 则不然。例如：
What you said yesterday is right.
三、宾语从句用以区分主语从句的几个特征(宾语从句语法请点击>>>>>高中英语语法宾语从句定义及用法）
1、引导词：whatwhichwhosewhenwhetherifwhere
2语序：宾语从句必须是用陈述语句。(名词性从句都是陈述语序)
如：I think that you must work harder.
宾语从句的引导词、连接词的区别、否定转移等现象。
补充：从句的语序永远是陈述句。
高二年级人教版英语Unit5重点句子的内容就是这些，相信大家一定需要了解人教版高二英语Unit5重点词汇讲解和人教版高二英语Unit5重点词汇讲解，希望对大家掌握基础有帮助。
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高中重点语法主语从句提升练习及答案
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