名词性从句讲义
【主语从句及引导词】
主语从句在复合句中作句子的主语。引导主语从句的词有从属连词that, whether, if；连接代词who, whoever, whom, what, whatever, whose, which；连接副词when, where, how, why等。
【例句呈现】
观察下列例句，指出其中所包含的主语从句及引导词:
1. What is needed for a long trip is careful preparation.
该句中主语从句是______________，引导词为_____。
2. That Jay Zhou will come to my city excites everybody.
该句中主语从句是______________，引导词为_____。
3. Whether we will travel abroad or not has not been decided.
该句中主语从句是______________，引导词为_____。
4. Whoever knows the secret mustn’t tell others.
该句中主语从句是______________，引导词为_____。
5. It remains a puzzle why dinosaurs died out suddenly long time ago.
该句中主语从句是______________，引导词为_____。
【观察总结】
通过分析上面例句，同学们可能会发现上面第5句中的主语从句似乎比较隐蔽。其实，这也是主语从句的一种呈现方式，即：当一个句子主语过长时，可以用it作形式主语，而把真正的主语或主语从句后移至句子末尾，以保持句子的平衡。注意观察下列例句中的划线部分：
It is not clear how the accident happened.
It is not hard to understand why he did so at that time.
It is a pity that you should have made such a careless mistake.
It is reported that more than thirty deaths were caused in the accident.
不难看出，虽然上面例句中都用it作形式主语，但句子结构却不尽相同。现将常见的由it作形式主语的句型总结如下：
1. It is + n. + that从句
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2. It is + adj. + that从句，常见此类形容词有：important, necessary, clear, certain, natural, strange, obvious, likely, impossible, possible 等。
3． It + 特殊动词 + that从句
It seems / appears ... that ... 似乎……
It happened (to sb.) that ... （某人）碰巧……
4． It + be + 过去分词+ 主语从句
It is said / reported / believed / suggested / known / proved that ...
【要点精讲】
1. what与that引导主语从句
观察下列例句，试着翻译例句并总结其规律。
(1) What you lack is self-confidence.
译为：_____________________
(2) That more and more students are admitted into universities is true.
译为：_____________________
(3) What is needed for the program is more wisdom.
译为：_____________________
从上面例句可以看出，that引导主语从句时，在句中具有“两不”原则：一、不作句子成分；二、没有实际意义。当它引导的主语从句置于句首时，that不能省略；如果用it作形式主语，而把主语从句放在句末时， that可以省略。而what引导的从句则恰恰相反，what在从句中的作用为：一、作句子成分；二、除了起到引导从句的作用外还要承担具体的意义。
【巩固练习】 用what或that填空。
(1) _____ he told us this morning was just a lie.
(2) _____ is important to us is enough time.
(3) It worries my mom _____ she is beginning to get a little fat.
(4) _____ we can’t get seems better than _____ we have.
2. whether与if引导主语从句
如果主语从句置于句首，不能用if引导，此时，需用whether。但如果用it作形式主语，而把主语从句放在句末时，也可以用if引导。
【巩固练习】 用whether或if填空。
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(1) It doesn’t matter _____ he will come or not.
(2) _____ we’ll go camping tomorrow depends on the weather.
(3) It was doubtful _____ Tom really saw Sharon.
(4) _____ Tom really saw Sharon was doubtful.
3. 其它引导词
连接代词who, which, whom, whose有各自的具体意义，起连接作用，同时在从句中充当主语、宾语、表语、定语等；whoever, whatever, whichever在意义上更为强调，常译为“无论……”；连接副词when, where, why, how等也有各自的意义，起连接作用，并在从句中作状语。
【高考链接】 从A、B、C、D四个选项中，选出可以填入空白处的最佳选项。
1. It is still under discussion _____ the old bus station should be replaced with a modern hotel or not.
(重庆2011)
A. whether B. when C. which D. where
2. The villagers have already known _____ we’ll do is to rebuild the bridge. (江西2011)
A. this B. that C. what D. which
3. _____ some people regard as a drawback is seen as a plus by many others. (北京2010)
A. Whether B. What C. That D. How
4. It never occurred to me _____ you could succeed in persuading him to change his mind. (陕西2010)
A. which B. what C. that D. if
5. It is uncertain _____ side effect the medicine will bring about, although about two thousand patients have taken it. (浙江2010)
A. that B. what C. how D. whether
Key:
【例句呈现】
1． What is needed for a long trip; what
2． That Jay Zhou will come to my city; that
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3． Whether we will travel abroad or not; whether
4． Whoever knows the secret; whoever
5． why dinosaurs died out suddenly long time ago; why
【要点精讲】
1. (1)你所缺乏的是自信。
(2)越来越多的学生将被大学录取的消息是真实的。
(3)这个项目所需要的是更多的智慧。
【巩固练习】
(1) What (2) What (3) that (4) What, what
2. 【巩固练习】
(1) whether / if (2) Whether
(3) whether / if (4) Whether
【高考链接】 1-5 ACBCB
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