1、3.主语从句1．定义：主语从句：在复合句中充当主语的句子叫主语从句例如：How he was successful is still a puzzle. 他是如何成功的仍然是个谜。2. 连接词的选用（1）that和what的选用that和what都可引导主语从句。what除起连接作用外，还在名词性从句中充当某些成分，可作从句的主语、宾语或表语。而that在名词性从句中不充当任何成分，无词义，只起连接词作用如：What he wants is a book. 他想要的是一本书That light travels in straight lines is known to a
2、ll. 众所周知，光线沿直线运行（2）if和whether的选用引导主语从句，不能用if，只能用whether。如：Whether we will hold a party in the open air tomorrow depends on the weather. 我们明天是否在户外开晚会要看天气而定（3）其它连接代词和副词的选用根据主语从句的具体意义，正确的选择who, which, when, where, why, how等连接词，这些连接词既有疑问含义，又起连接作用，同时在从句中充当各种成分如：When we shall hold our sports me
3、et is not decided. 我们何时举行运动会还没有决定。Who broke the glass yesterday is not clear. 还不清楚昨天谁打破了玻璃Which car you will choose to buy makes no difference. 你决定买哪一辆车都不会有任何区别（4）whatever / whoever的功用whatever, whoever在主语从句中不含疑问意义。它引导主语从句，并在从句中作主语、宾语、表语等。whatever = anything that; whoever = anyone who。要注意和
4、whatever, whoever引导的让步状语从句的区别如：Whoever breaks the law should be punished. （主语从句）（＝Anyone who breaks the law should be punished. ）Whoever breaks the law, he should be punished. （让步状语从句）（＝No matter who breaks the law, he should be punished. ）3. it构成的主语从句（1）由连词that引导的主语从句，在大多数情况下会放到句子的后面，而用代
5、词it作形式主语。如：It is well-known that the earth moves around the sun. 众所周知，地球围绕太阳转。【拓展延伸】需要注意的是，it作形式主语代替主语从句时，要注意和as引导的定语从句的区别。试比较：It was reported that the US was under the terrorist attack. （主语从句，有that，无逗号）As was reported, the US was under the terrorist attack. （定语从句，无that，有逗号）上两句意为“据报道，美国遭到
6、恐怖分子的袭击”（2）常见用it作形式主语的复合句结构It is a fact （a good idea / a pity / a shame / no wonder / good news…）that…如：It’s a pity that you missed the film. 你没有看那部电影真是太遗憾了 It is necessary （clear / true / strange/ important /wonderful / possible / likely…）that…需要注意的是，这类主语从句中，谓语动词很多为“（should）＋动词原形”，即要用虚拟语
7、气如：It is necessary that you （should）master the computer. 你很有必要掌握电脑It is important that a student learn English well. 学生学好英语很重要It’s clear that they badly need help. 很明显，他们急需援助It is likely that a hurricane will arrive soon. 飓风很可能马上就要到达了。It is reported （well-known / ho
