(1) 从属连词that。

例如：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。

例如：He looked just as he had looked ten years before. 他看起来还与十年前一样。

例如：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。

例如： 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

例如：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。