1．了解主语从句的概念和用法。
2．可以依据本节课的内容来完成一些习题。
▼ 定语从句：作定语的从句
I have a dog that is very cute. 我有一只可爱的狗
主语 谓语 宾语 定语从句〔句中做定语，限定修饰前面的名词dog〕
▼ 宾语从句：作宾语的从句，放在动词或介词后面
I think the dog is very cute. 我觉得这个狗很可爱
主语 谓语 宾语从句〔句中做think的宾语〕
▼ 状语从句：作状语的从句
I bought a dog because it’s very cute. 我买了一只狗，由于它很可爱
主语 谓语 宾语 状语语从句〔句中做状语，表缘由〕
那么，主语从句是？聪慧的人都能看出来——作主语的呗
主语从句结构及用法
在句子中担当主语的从句就叫做主语从句，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。通常结构为“引导词 + 主语 + 谓语 + 其他成分"。
一. 概念：在句子中担当主语的从句就叫做主语从句，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。
主语从句使用陈述语序，其通常结构为“引导词 + 主语 + 谓语 + 其他成分", 但当连接代词同时充当从句主语时，其结构为“连接代词 + 谓语 + 其他成分〞。
二. 引导词：
引导主语从句的词有连词：that, whether, if；连接代词：what, whatever, who, whoever, whom, whomever, whose, which, whichever；连接副词：when, whenever, where, wherever, how, however, why。
1. 连词that, whether, if引导的主语从句
that在主语从句中不作成分，没有意思，不能省略；whether和if虽不作句子的成分，但有“是否〞的意思，且if引导的主语从句不能位于句首。
That she is still alive is a consolation. 她还活着是使人感到宽慰的。
That she became an artist may have been due to her father's influence. 她成为画家可能
是受她父亲的影响。
Whether it will do us harm remains to be seen. 是否对我们有害还要看一看。
Whether they would support us was a problem. 他们是否会支持我们还是一个问题。
2. 连接代词what, whatever, who, whoever, which, whichever引导的主语从句
what, whatever, who, whoever, whom, whomever, whose, which, whichever在主语从句中起代词的作用，可以作主语、宾语、表语或定语，有详细的意思且不能省略。
What surprised us was that he passed the driving test.使我们感到惊异的是他通过了驾驶考试。
Whatever I have is yours. 我所拥有的一切都是你的。
歌语Who will go is not important. 谁将去是不重要的。
Whoever is here gets a prize. 不管谁来，都能获奖。
Which team will win the match is still unknown. 哪个队将赢得竞赛还不知道。
Whichever you chooseflashcs3 is OK. 不管你选哪一个都行。
3. 连接副词when, whenever, where, wherever, how, however, why引导的主语从句
when, whenever, where, wherever, how, however, why在主语从句中起副词的作用，作状语，有详细的意思且不能省略。
When we arrive doesn't matter. 什么时候到没有关系。
摄像头怎么打开Whenever you e is OK. 你无论何时来都行。
Where I spend my summer is no business of yours. 我在哪里过暑假不关你的事。
Wherever she wants to go is not allowed. 无论她想要去哪儿都是不被允许的。
How it was done was a mystery. 这是怎样做的是一个谜。
However late you e doesn’t matter. 无论你来的有多晚都没关系。
Why he did it wasn’t quite clear. 他为什么做那件事是不清晰的。
4. 用it作形式主语的主语从句
假如主语从句太长，为了防止句子结构头重脚轻，我们可以用it作形式主语，而把主语从句放在主句谓语局部之后。常见的结构有：
①It+is+形容词+that…，常见的形容词有known, clear, necessary, likely, unlikely, right, wrong, important, certain, obvious, strange, natural等。
That the earth turns around the sun is known to us all.
→It is known to us all that the earth turns around the sun.地球围着太阳转这一点是众所周知的。
Whether he will e or not is not clear.
→It is not clear whether /if he will e or not. 他是否要来还不清晰。
猫狗可以一起养吗②It+is+名词+that…，常见的名词有a pity, a shame, a fact, an honour, a mystery, a wonder, no wonder, good news, mon knowledge等。
It is a pity that he didn’t pass the exam. 他没有通过考试真圆满。
It is a wonder that he survived the crash. 他从坠机大事中幸存下来真是个奇迹。
It is no wonder that he has achieved so much success. 难怪他取得如此大的胜利。
③It+is+动词过去分词+that…，常见的过去分词有said, believed, reported, pointed out, hoped, thought, decided, ordered等。
It is said that he is a famous writer. 据说他是位闻名的作家。
It is reported that there will be a storm this afternoon. 据报道今日下午有暴风雨。
④It+特别动词+that…，常见的特别动词有seem, appear, happen, matter, turn out, occur to, make a difference等。
It seems that it is going to rain. 天看起来要下雨了。
It happened that I didn’t take any money with me. 碰巧我身上没带钱。
It occurred to me that I didn’t close the window. 我突然想起我没有关窗户。
⑤It+使令性动词+sb.+，常见的动词有worry, shock, surprise, satisfy, upset等。
It upset him a lot that he was fired. 他被解雇了使他很难受。
It surprised me that she brought up three children on her own.她单独抚养三个孩子使我感到惊讶。
主语从句不行位于句首的五种状况
爨龙颜首先我们大家都明白在复合句子中起名词作用的句子叫名词性从句。简洁把它理解成名词，但形式是一个句子。那主语从句就是在句中作主语，主语从句的位置与陈述句中主语位置相同的
(1) if 引导的主语从句不行居于复合句句首。
It is uncertain if he will leave for Beijing tomorrow.
(2) It is said , (reported) …结构中的主语从句不行提前。例如：
It is said that President Jingo will visit our school next week. (right)
That President Jiang will visit our school next week is said. (wrong)
(3) It happens…, It occurs… 结构中的主语从句不行提前。例如：
whether是什么意思It occurred to him that he failed in the examination. (right)
That he failed in the examination occurred to him. (wrong)
(4) It doesn’t matter how/whether …结构中的主语从句不行提前。例如：
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