表句就是”表句是个句子”,同理,宾语从句,定语从句都这样理解.
从句放在连系动词之后,充当复合句中的表语/
下面是我找到的材料,参考一下吧.
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基本概念
1． 定义表语从句例句：用作表语的从句叫做表语从句。
2． 构成：关联词+简单句
3． 引导表语从句的关联词的种类：
(1) 从属连词that。如：
The trouble is that I have lost his address. 麻烦是我把他的地址丢了。
(2) 从属连词whether, as, as if。如：
He looked just as he had looked ten years before. 他看起来还与十年前一样。
The question is whether they will be able to help us. 问题是他们是否能帮我们。
注：从属连词if一般不用来引导表语从句，但as if却可引导表语从句，如：
All this was over twenty years ago, but it´s as if it was only yesterday.
这都是20多年前的事了，但宛如昨天一样。
能跟表语从句的谓语动词一般为系动词be, seem, look等。如：
It looked as if it was going to rain. 看起来天要下雨了。
(3)连接代词who, whom, whose, what, which, whoever, whatever, whichever
连接副词 where, when, how, why。
如：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 how he did it. 问题是他是如何做此事的。
That was what she did this morning on reaching the attic. 那就是她今晨上了阁楼干的。
引导词that whether,连接代词和连接副词,关系代词 what,还有 as if because等.语序：主语+系动词+表语从句.时态：一般情况下从句的时态先于或者等于主句的时态
在What made him proud was that more than 80% of the fruit had been fresh一句中，What made him proud 是主语从句，that more than 80% of the fruit had been fresh是表语从句。本句属于：主语（从句）＋be+表语（从句）你的疑问是：如果What made him proud 是主语从句，那它就属于“从句”的性质了，所以句子就没有“主句”了，对不对？通俗地说吧，其实“主句”也是一种从句，只不过它是“主要的从句”，所以我们就叫它“主句”了。