复合句由一个主句和一个或一个以上的从句构成，指的是含有两个或更多的主谓结构的句子，其中有一个（或更多）主谓结构充当句子的某一（些）成分，如主语、宾语、表语、定语、状语、同位语等。复合句根据从句类型可以划分为很多种，小编这次就先来给大家讲讲表语从句的相关知识吧。
引导表语从句的词有连词that, whether，连接代词和连接副词，关系代词型what，以及as if, as though, because等连词。
1. 由that引导
The fact is that he doesn’t really try. 事实是他没有做真正的努力。
The trouble is that I have lost his address. 麻烦的是我把他的地址丢了。
My suggestion is that we should tell him. 我的建议是我们应该告诉他。
His sole requirement was (is) that the system work. 他唯一的要求是这个制度能起作用。
My idea is that we should start making preparations right now. 我的意见是我们马上就开始做准备工作。
2. 由whether引导
The question is whether the film is worth seeing. 问题是这部电影是否值得看。
【注意】whether 可引导表语从句，但与之同义的if却通常不用于引导表语从句。
3. 由连接代词引导
You are not who I thought you were. 你已不是我过去所想像的人。
The problem is who we can get to replace her. 问题是我们能找到谁去替换她呢。
The question is who (m) we should trust. 问题是我们应当相信谁。
What I want to know is which road we should take. 我想知道的是我们应走哪条路。
4. 由连接副词引导
The problem is how we can find him. 问题是我们如何找到他。
That was when I was fifteen. 这是我15岁时发生的事。
That’s where I first met her. 那就是我第一次遇见她的地方。
That’s why he didn’t come. 这就是他没有来的缘故。
That’s why I object to the plan. 这就是我反对这个计划的原因。
That’s where you are wrong. 这就是你不对的地方。
5. 由关系代词型what引导
That’s what I want to stress. 这是我想强调的。
That’s what we are here for. 我们来这里就为了这个。
Fame and personal gain is what they’re after. 他们追求的是名利。
He is no longer what he was. 他已经不是以前的他了。
6. 由as if / as though引导
It isn’t as if you were going away for ever. 又不是你离开不回来了。
Now it was as though she had known Millie for years. 现在好像她认识米莉已有好多年了似的。
It is not as though we were poor. 又不是我们家里穷。
7. 由because引导
It is because I love you too much. 那是因为我太爱你了。
That’s because you can’t appreciate music. 这是因为你不能欣赏音乐。
If I’m a bit sleepy, it’s because I was upall night. 如果我有点困，是因为一夜没睡。
It's because I passed a slip of paper for John to Helen in class. 这是因为我在上课中替约翰传纸条给海伦。
【注意】because 可引导表语从句，但与之同义的since, as, for等也不用于引导表语从句。
以上就是表语从句的相关知识，大家都看明白了吗？表语这个概念虽然经常让人摸不清头脑，但实际上，掌握好表语从句的关键依旧是掌握好引导词的用法，所以各位学习者们可以参考着例句对引导词的用法进行理解记忆。