请问什么是表语从句比如-No,that's where they're mistaken

请问什么是表语从句
比如-No,that's where they're mistaken

表语从句在句中做表语,用来表明事物的状态,比如外观,大小,形状,颜色,材质等等.表语从句就是一个句子做表语.
表语从句可以分为六 种:
一、由that引导的表语从句
The trouble is that he misunderstood me.麻烦的是他误解了我.
有时,引导表语从句的连词that可以省略
The truth is (that) I didn’t finish my term essay. 事实是我没有写完学期论文.
二、由连接代(副)词引导的表语从句
连接代词who, whom, whose, what, which, whoever, whatever, whichever；
连接副词where, when, how, why.
That was what she said this morning in her bedroom.那就是她今天早晨在卧室 中说的.
三、由关系代词型的what引导的从句
I want to be a teacher. That’s what I want to be.我想当老师,那是我的志愿.
四、关联词是连词because
比较下面这两个句子:
I was angry. That was because he didn’t understand me.我生气是因为他不理解 我.(表语从句强调原因)
That’s why he got fired from that firm. 那正是他被公司解雇的原因.(表语从句 强调结果)
注意:reason作主语或主语中包含事件的 起因时,后面的表语从句表示原因时要用 that来引导,而不用because
That is why ...是常用句型,其中why引导 的从句在句中作表语,该句型通常用于针 对前面已经说过的原因进行总结.
1. That is the reason why ...That is the reason why ...与That is why ...是同义的, 但是从语法结构上讲,That is the reason why ...中的why引导的是一个定语从句, 将其中的the reason去掉后则与That is why ...结构一样了
2. That is because ...That is because ...也 是一个常用句型.That is because ...句型 中,连词because引导的从句作表语,That is because ...与That is why ...之间的不同 在于That is because ...指原因或理 由,That is why ...则指由于各种原因造成 的结果
He did not read Harry Potter last night. That is because he had to help his mother to do the housework. 昨天晚上 他没有读《哈里波特》,那是因为他得帮 助他妈妈做家务.
五、关联词是从属连词whether, as, as if
The question remains whether we can win the majority of the people.问题是我 们能否赢得大多数民众的支持.
六. 使用虚拟语气的表语从句
在表示建议、劝告、命令含义的名词后 的表语从句,谓语动词需用“should+动 词原形” 表示,should可省略.常见的词 有：advice,suggestion,order, proposal,plan,idea等.
My suggestion is that we （should） start early tomorrow.我的建议是我们明 天一早就出发.