不明白主语从句里面作成分那些?

1.主语从句的语序
　　主语从句要求使用陈述句语序,而非一般疑问句语序.如：
　　What surprised me most was that the little girl could play the violin so well.
　　使我感到惊讶的是这个小女孩的小提琴拉得太好了.
　　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 all.
　　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 meet 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.
　　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*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 / hoped / thought / expected /said /believed/decided /suggested /ordered…）that…如：
　　It is said that he was killed in the earthquake.据说他在地震中丧生了.
　　It seems （happened / appears / doesn’t matter / makes no difference / …）that …如：
　　It seems that they will win the game.
　　看起来他们好像会赢得这场比赛.
　　It makes no difference whether he will attend the meeting or not.
　　他是否会参加会议都无关紧要.
　　摘自 考试报