从句：(从句=引导词+主谓)从句指复合句中不能独立成句，但具有主语部分和谓语部分，有that、who、what、when、how等引导词引导的非主句部分。名词性从句在句子中起名词作用的句子。那么名词在句子中可以做什么成分呢？名词在句子中可以做“主语”、“宾语”、“表语”、“同位语”

名词性从句的分类

名词性从句分类如下：主语从句：在句子中充当主语的从句。宾语从句：在句子中充当动词或介词宾语的从句。表语从句：在句子中充当系动词表语的从句。同位语从句：在句子中修饰某一名词的从句，一般位于该名词的后面，解释说明该名词的具体内容。

主语从句

"The fact" is obvious.这事实是明显的。The fact是主语那么我们将"The fact"改为一个具体的事件则是
"That the rabbit ate a carrot" is obvious.
此时这就是由"that"引导的主语从句，翻译为"兔子吃了胡萝卜是明显的".
但是这样翻译会有歧义，到底是兔子是明显的，还是吃了胡萝卜是明显的。
但是因为句子开头使用了"that"做引导词，所以老外们一看到这个信号就会本能意识到，哦这是个从句啊，只是整个句子的一部分而已。
所以我们中文翻译时就需要加个标志，翻译为“兔子吃了胡萝卜这件事实明显的”总结："That the rabbit ate a carrot" is obvious."That the rabbit ate a carrot" 是主语有上述可知，说白了，主语从句就是句子主语由从句充当，其他成分则保持不变。

不确定的信息的主语从句

不确定信息1.兔子"是否"吃了胡萝卜是明显的。     "Whether" the rabbit ate the carrot is obvious.2.兔子"哪里"吃了胡萝卜是明显的。     "Where" the rabbit ate the carrot is obvious.3.兔子"什么时候"吃的胡萝卜是明显的。  "When" the rabbit ate the carrot is obvious.4.兔子"怎样"吃地胡萝卜是明显的。     "How" the rabbit ate the carrot is obvious.5."谁"吃了胡萝卜是明显的。          "Who" ate the carrot is obvious.6.兔子吃了"什么"是明显的            "What" the rabbit ate is obvious.

形式主语

如果上面的主语从句很长如下："That the hungry rabbit had already eaten a carrot for dinner this evening" is obvious.按照语序翻译“这只饥饿的兔子今天晚上已经吃了一根胡萝卜这很明显”。这样的句子表达起来很费劲，让人听了半天才知道，原来只是像表达这件事很明显。这就导致了头重脚轻的句式，英语母语人不会这样表达。英语母语人这样表达It is obvious "that the hungry rabbit had already eaten a carrot for dinner this evening".这里开头的It不是平时指代物体的代词“它”，而是指代后面的从句，本身没有实际意义，所以被称为"形式主语"。It代表之后的真正的主语，也就是说放在句子后面的从句才是真正的主语。所以 It is obvious that the rabbit ate a carrot.应该翻译为"很明显，兔子吃了胡萝卜"而千万不要按顺序翻译为“它很明显，兔子吃了胡萝卜”

That the rabbit ate a carrot is a secret.
That the rabbit ate a carrot was discussed.
That the rabbit ate a carrot happend.可改为It is secrte that the rabbit ate a carrot.
It was discussed that the rabbit ate a carrot.
It happened that the rabbit ate a carrot.不确定信息则可改为
"Whether" the rabbit ate the carrot is obvious.    It is obvious whether ....
"Where" the rabbit ate the carrot is obvious.      It is obvious where ....
"When" the rabbit ate the carrot is obvious.       It is obvious when ....
"How" the rabbit ate the carrot is obvious.        It is obvious how ....
"Who" ate the carrot is obvious.                   It is obvious who ....
"What" the rabbit ate is obvious                   It is obvious what ....

宾语从句

宾语从句就是从句在复杂句中做宾语，宾语从句也有包含确定信息和不确定信息。宾语从句确定信息I saw "that the rabbit ate a carrot".(我看见这兔子吃了根胡萝卜。)宾语从句不确定信息I saw "whether" the rabbit ate the carrot.I saw "where" the rabbit ate the carrot.I saw "when" the rabbit ate the carrot.      I saw "how" the rabbit ate the carrot.I saw "who" ate the carrot.I saw "what" the rabbit ate.注意：除了某些介词参与的情况，从句的引导词基本都在从句的开头，否则干嘛就引导词呢，引导从句嘛，肯定是在前面引导咯 。而其他的词遵照正常的陈述语序，基本也和中文一致。

that引导词可以省略

I know (that) the rabbit ate a carrot.(that可以省略)
因为可以省略that所以不要误以为这是一个简单句，不要认为这个简单句中为什么有know和ate两个动词呢，其实know是主句里的动词，而ate是从句里的动词 。注意只有that可以省略，其他的what、who、which、when、where、how等不能省略。

宾语从句的否定

I think (that) the rabbit is smart.(我认为这兔子很聪明)
I believe (that) you will give me some coins.(我相信你会给我投币)
I expect (that) you will give this video a thumbs-up.(我指望你给我视频点赞)变为否定时，否定往往是加在谓语动词前,而非从句中
I do not think (that) the rabbit is smart.
I do not believe (that) you will give me some coins.
I do not expect (that) you will give this video a thumbs-up.以下表达式错误的
I think (that) the rabbit is not smart.
I believe (that) you would not(won't) give me some coins.
I expect (that) you would not(won't) give this video a thumbs-up.