名词性从句---主语从句
1. What is needed for the space trip is careful preparation.
2. Her wish is that she can lose weight soon. 
3. I think that woman can reach every high achievements in many fields of science.
4. We were very excited at the news that our team had won.   
引导名词性从句的关联词可分为三类：
一．从属连词：that无任何词意
whether, if均表示“是否”表明从句内容的不确定性
as if ,as though均表示“好像”,“似乎”以上在从句中均不充当任何成分
二．连接代词：what, who, whom, which,whose, whatever, whoever, whichever作主宾表定 
三．连接副词：when, where, how, why作状语 
I. 主语从句
1.定义：在句子中担当主语的是一个从句,这个从句就叫做主语从句;
2.位置：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;
3.引导主语从句的关联词：
1从属连词that,whether,if 在从句中不充当成分,仅起连接作用
That Jack won the match yesterday surprised us.
Whether he’ll come here isn’t clear. 此处不能用if
2连接代词who, whom, whose, what, which, whoever, whatever, whichever充当主宾表定
weight的所有形式What she did is not known.
Whoever comes is welcome.
3连接副词 where,when,how,why在从句中充当状语
How this happened is not clear to anyone.
When the meeting will be held is decided by our manager.
4.有时为了避免头重脚轻,常用it作形式主语,而把真正主语放在句子末尾;
How the book will sell depends on its author.
= It depends on its author how the book will sell.
That he is the best student in the class is obvious.= It is obvious that he is the best student in the class.
用it作形式主语的几种常见结构：
1 It is ＋ 名词 ＋ 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 ＋ 从句
It is natural that… 很自然 It is strange that… 奇怪的是…
3 It is ＋ 不及物动词 ＋ 从句
It seems that… 似乎… It happened that… 碰巧…
It appears that… 似乎…
4 It ＋ 过去分词 ＋ 从句
It is reported that… 据报道… It has been proved that… 已证实…
It is said that… 据说…
注意：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;例子见上面
2 It is said , reported …结构中的主语从句不可提前;
例如：It is said that President Xi 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
5.语序：主语从句用陈述语序;关联词位于句首不能省略
How he became a great scientist is known to us all.
Who the watch belongs to is unknown.
That he finished writing the composition in such a short time surprised us all.
6.主语从句中注意的事项：
1主语从句后的谓语动词一般用单数;
Whatever he says is of no importance.
Whoever says this is wrong.
但谓语动词用单数还是复数,不可一概而论,而要视句子的意义而定
What I need is money.
What I need are books.
2what 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则不作任何成分;
What you said yesterday is right.
That she is still alive is a consolation.
3it作形式主语和it用于强调句的比较：
it作形式主语代替主语从句,主要是为了平衡句子结构,主语从句的连接词没有变化；而it用于强调句则是对句子某一部分进行强调,无论强调的是什么成分,都可用连词that;被强调部分指人时也可用who/whom;
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.
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  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;
It is still a mystery what caused the accident.
It is a mystery that his death remained.
4whether与if
whether引导主语从句时,常置于句首此时whether不能用if代替,也有后移的用法此时whether可以用if代替
Whether they will come is not yet known.
It is not yet known whether/if they will go there.
whether和if的区别还有：
1. 引导表语从句用whether
The question is whether you should accept it.
2. whether可以引导从句作介词的宾语
I’m not interested in whether they’ll go or not.
It depends on whether we have got enough money.
3. whether可以直接跟动词不定式连用
I didn’t know whether to laugh or to cry.
She hasn’t decided whether to go or not.
4. 与or not连用时,只能用whether;
I don't know whether I should go there or not.
随堂练习：
1.    has helped to save the drowning girl is worth praising.
  A. Who      B. The one    C. Anyone      D. Whoever
2. It was    he said      disappointed me.
  A. what ; that    B. that; that    C. what; what    D. that; what
3.     we’ll go camping tomorrow depends on the weather.
  A. If        B. Whether      C. That        D. Where

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