語法 | 表語從句的引導詞用法簡述
表語從句和其他英語中的從句一樣，有很多不同含義和不同用法的引導詞，下面，小編就來爲大家講解一下表語從句的引導詞：
1.從屬連詞：that / whether /as if /as though/as/because
(1) that引導表語從句本身沒有詞義，在句中只起連接作用，不充當句子成分，一般不能省略。
That fact is that more than seventy percent of the earth’s surface is covered by water.
連接詞that一般不能省略，但當主句中含動詞do的某種形式時，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邊去感謝他。
(2) whether引導表語從句表示“是否”,但不充當句子的成分。
The question is whether we can finish our work by tomorrow evening.
if 與whether均意爲“是否”，但引導表語從句時，只能用whether, 不能用if。
(3)as if/though“好像”，引導表語從句時要注意語態.
如果句中的情況與事實不相符，從句多用虛擬語氣。如果從句表示與現在事實相反,謂語動詞用一般過去式；如果從句表示與過去事實相反時,謂語動詞要用“had + 過去分詞”，如果從句表示將來的可能性不大，用would (might ,could )+動詞原形.
Li Lei is now in a new jacket. He looks as if he were an American boy. (現在事實相反)
The girl is giving us a vivid description of the moon. It seems as if she had been to the moon many times. （與過去事實相反）
It looks as if it might rain. （與將來事實相反）
但是，如果as if/though引導的表語從句所表示的與事實相符，從句則用陳述語氣。
The clouds are gathering. It looks as if is going to rain.
(4) as引導表語從句
He looked just as he had looked ten years before.
他看起來還與十年前一樣。
(5) because引導表語從句
常用結構：This/That/It is/was because····
That is because I don’t like Chinese.
2.連接代詞：who/whom/whose/what/which/whoever/whatever/whichever/whomever，在表語從句中做主語、賓語、表語和定語。
Tom is no longer what he used to be. (what做表語)
The problem is who is fit for this job. (who做主語)
This is what I want to tell you. (what做賓語)
The problem is whose work is the best. (whose做定語)
3.連接副詞：when/where/how/why，在表語從句中做狀語。
The question is how he did it. 問題是他是如何做此事的。
The question is where we can live. 問題是我們能住在哪兒。
以上就是表語從句的引導詞的所有分類和用法了，希望在今後的學習和生活中能幫到大家。喜歡就收藏吧~
