1.定義：用作表語的從句叫做表語從句。
2.構成：關聯詞+簡單句
3.引導表語從句的關聯詞的種類：
（1）從屬連詞that.
如：The trouble is that I have lost his address.
麻煩是我把他的地址丟了。
（2）從屬連詞whether，as，as if.
如：He looked just as he had looked ten years before.
他看起來還與十年前一樣。
The question is whether they will be able to help us.
問題是他們是否能幫我們。
注：從屬連詞if一般不用來引導表語從句，但as if卻可引導表語從句，如：
All this was over twenty years ago, but it‘s as if it was only yesterday.
這都是20多年前的事了，但宛如昨天一樣。
能跟表語從句的謂語動詞一般為系動詞be，seem，look等。
如：It looked as if it was going to rain.
看起來天要下雨了。
（3）連接代詞who，whom，whose，what，which，whoever，whatever，whichever
連接副詞where，when，how，why.
如：The problem is who we can get to replace her.
問題是我們能找到誰去替換她呢。
The question is how he did it.
問題是他是如何做此事的。
That was what she did this morning on reaching the attic.
那就是她今晨上了閣樓干的。
難點釋疑：
1.連詞because可引導表語從句。
如：I think it is because you are doing too much.
我想這是因為你做得太多。
2.在一些表示“建議、勸說、命令”的名詞后面的表語從句中，謂語動詞用虛擬語氣。should+動詞原形表示，should可省略。
My suggestion is that we (should) start early tomorrow.
我的建議是我們明天一早就出發。
