名詞性從句，即指性質(zhì)相當(dāng)于名詞的從句，它包括主語從句、賓語從句、表語從句和同位語從句。從高考的考查的實際情況來看，名詞性從句的連接詞是高考的熱點，也是考查的重點，這不僅體現(xiàn)在單項填空中，而且在完形和閱讀中對長難句的分析也是理解文章語意重要法寶。因此這是每個高中學(xué)生必須掌握的語法項目。 一、引導(dǎo)名詞性從句的連接詞
引導(dǎo)名詞性從句的連接詞可分為三類：
連詞：that ，whether, if ，as if ,as though等
以上在從句中均不充當(dāng)任何成分
連接代詞：what, whatever, who, whoever, whom,
whose, which. whichever, whomever等
連接副詞：when, where, how, why等
二、名詞性從句的一般引導(dǎo)詞
1. 連接詞 that 只起連接作用，沒有任何意思，也不充當(dāng)句子成分，在賓語從句中可省略，但引導(dǎo)其他名詞性從句時通常不省略。如：
I hope (that) you enjoy your holiday.
That he likes you is very obvious.
That-從句作主語通常用it作先行詞，而將that-從句置于句末。如：
It is quite clear that the whole project is doomed to failure.
It's a pity that you should have to leave.
用it作形式主語的that-從句有以下四種不同的搭配關(guān)系，其重要句型歸納如下：
a. It + be +形容詞+ that-從句
It is necessary (important, natural, strange, etc.) that …
It is necessary that… 有必要……
It is important that… 重要的是……
It is obvious that… 很明顯……
b. It + be + -ed 分詞+ that-從句
It is suggested (requested, proposed, desired, etc.) that…
It is believed that… 人們相信……
It is known to all that… 從所周知……
It has been decided that… 已決定……
c. It + be +名詞+ that-從句
It is a pity (a shame, no wonder, etc.) that…
It is common knowledge that… ……是常識
It is a surprise that… 令人驚奇的是……
It is a fact that… 事實是……
d. It +不及物動詞+ that-分句
It appears that… 似乎……
It happens that… 碰巧……
It occurred to me that… 我突然想起……
2. 連接詞 whether 也不充當(dāng)句子成分，但有自己的意思，表示“是否”；引導(dǎo)賓語從句時。 比較：
whether與if 均為"是否"的意思。 但在下列情況下，whether 不能被if 取代：
1. whether引導(dǎo)主語從句并在句首
2. 引導(dǎo)表語從句、同位語從句
3. whether從句作介詞賓語
4. 直接與"or not"連用
5. 與不定式連用
Whether he will come is not clear.
He asked me whether I would show him the way.
Whether it will do us harm remains to be seen.
3. 連接代詞 who(m), whose, which, what 等，均有各自的意義，在從句中作主語、賓語、定語等。如：
That’s what she wanted to do .
Who will join in the game doesn't matter.
Tell me which one you like best.
4. 連接副詞 when, where, why, how 等，也各自有自己的意義，在從句中作狀語。如：
The question is how we should carry out the plan.
When she’ll be back depends much on the weather.
Why he did it will remain a puzzle forever.
三、名詞性從句的重要引導(dǎo)詞
1. what 用于引導(dǎo)名詞性從句是一個十分重要的引導(dǎo)詞，它可引導(dǎo)主語從句、賓語從句和表語從句，但不用于引導(dǎo)同位語從句。它引導(dǎo)的名詞性從句有兩個意思是：一是表示“什么”，帶有疑問意味；二是表示“…所…的”，相當(dāng)于一個先行詞后接一個關(guān)系代詞。如：
I don’t know what you want.
I don’t know what you want is this.
2. what 引導(dǎo)名詞性從句時可用作限定詞，其后修飾名詞。如：
I gave him what books I had.
He gave me what money he had about him.
注：what 后的名詞可以是復(fù)數(shù)名詞或不可數(shù)名詞，但通常不能是單數(shù)可數(shù)名詞。
What friends she has are out of the country.
We gave him what (little) help we could.
3. whoever, whatever, whichever 等也可引導(dǎo)名詞性從句，其意分別為“所…的一切事或東西”、“任何…的人”、““…的任可人或物”等。如：
Whoever wants the book may have it.
I’ll do whatever I can to help him.
Buy whichever is the cheapest .
注意以下受漢語意思影響而弄錯的句子：
任何人來都?xì)g迎。
誤：Who comes will be welcome. / Anyone comes will be welcome.
正：Whoever comes will be welcome. / Anyone who comes will be welcome.
另外，它們也可引導(dǎo)讓步狀語從句，其意為“無論…”、“不管…”，其意相當(dāng)于 no matter who [what, which]。如：
Whatever happens, you must be calm.(whatever = no matter what)
He won't eat you, whoever he is. (whoever = no matter who)
4. why 與 because 的用法區(qū)別。兩者均可引導(dǎo)表語從句，但前者強(qiáng)調(diào)結(jié)果，后者強(qiáng)調(diào)的原因。如：
I had a cold. That’s why I didn't come.
I didn’t come. That’s because I had a cold.
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