(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.
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。
解释：
1. 连词because可引导表语从句。如：
I think it is because you are doing too much. 我想这是因为你做得太多。
2. 在一些表示"建议、劝说、命令"的名词后面的表语从句中，谓语动词用虚拟语气。should+动词原形表示，should可省略。如：
My suggestion is that we (should) start early tomorrow. 我的建议是我们明天一早就出发。
(1) 从属连词that。 如：That they were in truth sisters was clear from the facial resemblance between them.
(2) 从属连词whether。如：
Whether he’ll come here isn’t clear. 他是否会来这里还不清楚。
(3) 连接代词who, whom, whose, what, which, whoever, whatever, whichever
连接副词 where, when, how, why。如：
What she did is not yet known. 她干了什么尚不清楚。
How this happened is not clear to anyone. 这事怎样发生的，谁也不清楚。
Whoever comes is welcome. 不论谁来都欢迎。
Wherever you are is my home ---- my only home. 你所在的任何地方就是我的家----我唯一的家。
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