表语从句和其他英语中的从句一样，有很多不同含义和不同用法的引导词，下面，小编就来为大家讲解一下表语从句的引导词：
?
1.从属连词：that / whether /as if /as though/as/because
(1) that引导表语从句本身没有词义，在句中只起连接作用，不充当句子成分，一般不能省略。
That fact is that more than seventy percent of the earth’s surface is covered by water.
连接词that一般不能省略，但当主句中含动词do的某种形式时，that可以省略。
What I want to do is (that) I can go up to him and thank him. 我想做的事是走到身边去感谢他。
(2) whether引导表语从句表示“是否”,但不充当句子的成分。
The question is whether we can finish our work by tomorrow evening.
if 与whether均意为“是否”，但引导表语从句时，只能用whether, 不能用if。
(3)as if/though“好像”，引导表语从句时要注意语态.
如果句中的情况与事实不相符，从句多用虚拟语气。如果从句表示与现在事实相反,谓语动词用一般过去式；如果从句表示与过去事实相反时,谓语动词要用“had + 过去分词”，如果从句表示将来的可能性不大，用would (might ,could )+动词原形.
Li Lei is now in a new jacket. He looks as if he were an American boy. (现在事实相反)
The girl is giving us a vivid description of the moon. It seems as if she had been to the moon many times. （与过去事实相反）
It looks as if it might rain. （与将来事实相反）
但是，如果as if/though引导的表语从句所表示的与事实相符，从句则用陈述语气。
The clouds are gathering. It looks as if is going to rain.
(4) as引导表语从句
He looked just as he had looked ten years before.
他看起来还与十年前一样。
(5) because引导表语从句
常用结构：This/That/It is/was because····
That is because I don’t like Chinese.
2.连接代词：who/whom/whose/what/which/whoever/whatever/whichever/whomever，在表语从句中做主语、宾语、表语和定语。
Tom is no longer what he used to be. (what做表语)
The problem is who is fit for this job. (who做主语)
This is what I want to tell you. (what做宾语)
The problem is whose work is the best. (whose做定语)
3.连接副词：when/where/how/why，在表语从句中做状语。
The question is how he did it.?? 问题是他是如何做此事的。
The question is where we can live.? 问题是我们能住在哪儿。
?
以上就是表语从句的引导词的所有分类和用法了，希望在今后的学习和生活中能帮到大家。喜欢就收藏吧~
