名词性从句是英语语法中的重要组成部分，它们在句子中充当主语、宾语、表语或同位语等成分。引导词是连接主句和从句的关键，它们的选择和使用对句子意义的表达至关重要。
1. that引导名词性从句时只起连接从句的作用,本身没有任何意义,因此在从句中不充当任何句子成分,它的使用须注意以下几点:
A. 引导宾语从句时,that常可省略,但如果主句后跟有并列宾语从句时,只能省略第一个that;若宾语从句前插有别的从句时,that也不能省略。例如:
He told me (that) he was all right and that he would come to see me when he was free. 他告诉我说他很好,并说在他有空时来看我。
B. that引导主语从句位于句首时不可省略.如果it作形式主语,而that从句置于句末, 这时that可以省略。例如:
That he has lost his work is not true. 他丢了工作不是真的。
=It is not true (that) he has lost his work.
C.当主语为the reason时,注意应用that 引导其表语从句,不能受汉语影响而误用because。例如:
The reason why he was late was that he missed the early bus. 他迟到的原因是他没赶上早班车.(此句中的that不可用because代替)
D.引导同位语从句时,切不可错用which。例如:
Word has come that some American guests will come to visit our school next week. 有消息说下周将有一些美国客人来我校参观。
2. what与which引导名词性从句时都在从句中充当句子的某一成份,如主语、表语、宾语或定语,其区别是:what表示泛指的事物,常译为"什么"或"所……的事物", whatever是它的强 语势"无论什么";which表示特定事物中的"哪一个(些)",一般情况下在从句中充当定语,后接名词,在一定的语境中,它所修饰的名词可以省略,whichever是它的强语势"无论哪一个(些)"。例如:
I believe what (whatever) he says. 我相信他说的(不管他说什么我都相信)。
I will give her which (whichever) book she likes on the shelf. 这个书架上的(任何一本)书,只要她喜欢,我都会给她。
在引导名词性从句时,在句中作主语时用who,意思是"谁",含有疑问意味,whoever是它的强语势"无论谁",不含有疑问意味。作宾语时用whom, 其相应强语势为whomever。判别时要根据句意以及在句中的语法功能来决定该用哪个引导词。例如:
Who has taken away my bag is unknown.谁拿走了我的包还不知道。(若用Whoever显然句意不通)
Whoever wants to see this film can go with us tonight. 无论谁想看这部电影今晚可以和我们一起去.(Whoever wants 相当于Anybody who wants,意为"凡是想……的人"。这里不可换为Who。)
Have you decided whom you are to nominate as your candidate? 你们是否已经决定提名谁作侯选人了?
You can give the ticket to whomever you like. 你可以把票给任何你想给的人。
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