that引导的主语从句(一)当主语从句本身不缺成分时,就会使用that来连接。
此时,that只起连接作用,但不能省略。如:That he will come to our village tomorrow surprises us all. (他要来我们村,让我们都感到很惊讶。)That she used to be a spy is known to all. (大家都知道,她过去是个间谍。)这种情况下,因为主语从句往往比谓语部分更长,会导致整个句子头重脚轻,所以经常会用it作为形式主语来替换主语从句,而把主语从句放到句末。此时,that也只起连接作用,但可以省略。比如,以上两个句子就存在这个问题,所以一般都会改为:It surprises us all (that) he will come to our village tomorrow.It is known to all (that) she used to be a spy.(二)如果句子是疑问句,则必须用带形式主语it的结构。如:That she is our English teacher is true. (她是我们的英语老师,是真的。)That he has been there twice is a fact. (他去过那儿两次了,是真的。)这两句话如果改为一般疑问句时,不能这么改:错误:Is that she is your English teacher true?错误:Is that he has been there twice a fact?而是要改为含有形式主语it的句子:Is it true that she is your English teacher?Is it a fact that he has been there twice?(三)在形式主语it引导的主语从句结构“It is+形容词/名词/名词短语等+that主语从句”中,如果is后面的表语是表示重要或必要等(如important、necessary、a necessity等)含义时,that从句中的谓语动词一般要采用“should+do”的虚拟语气形式,should经常省略。如:It is imperative that we (should) make a quick decision. (我们要尽快做出决定。)It is necessary that we (should) learn English well. (我们必须学好英语。)二、if/whether引导的主语从句当主语从句本身含有是否的意思时,连接词必须用if或whether。但是,如果主语从句位于句首时,只能用whether,不能用if。如:Whether it will do good to us remains to be seen. (是否对我们有害还要看一看。)这种情况下,因为主语从句也比较长,会导致头重脚轻的情况,所以也经常用形式主语it来代替,而把主语从句放到句末去。此时,连接词除了用whether外,也可以用if。如上面的句子就可以改为:It remains to be seen if/whether it will do good to us.再比如:Whether the band would visit our city was still a mystery. (这个乐队是否会来我们城市仍然是个谜。)上面的句子可以改为:It was still a mystery if/whether the band would visity our city.三、连接代词引导的主语从句常用来连接主语从句的连接代词有:who、whom、whose、which、whoever、whomever、whichever等。这些连接代词在从句中有的作主语,有的作宾语,有的作定语。如:作主语:Who won the game hasn't been announced yet. (谁赢得了比赛,还没宣布。)作宾语:Whom you talked to just now will be confirmed later. (你刚才跟谁说话了,之后会证实的。)作定语:Whichever nation explodes an atomic bomb will engage the whole world in war. (无论哪个国家使用原子弹都会使全世界卷入战争。)为了避免头重脚轻,这种情况下的主语从句也经常用形式主语it来代替,而把主语从句放到句末。但是,连接代词始终都不能省略。如上面的两句话可以改为:It hasn't been announced yet who won the game.It will be confirmed later whom you talked to just now.It will engage the whole world in war whichever nation explodes an atomic bomb.四、连接副词引导的主语从句能够用来连接主语从句的连接副词主要有:when、where、why、how等。这些连接副词在主语从句中作状语。如:When they will arrive at the station doesn't matter. (他们何时到站没有什么关系。)How the accident happended is still unknown. (这场事故是怎么发生的,还不清楚。)Why he was absent from the meeting remains a mystery. (他为什么没有参加会议仍然是个谜。)Where I will spend my summer is none of your business. (我在哪里过暑假不关你的事。)为了避免头重脚轻,上面的句子可以改为:It doesn't matter when they will arrive at the station.It is still unknown how the accident happended.It remains a mystery why he was absent from the meeting.It is none of your business where I will spend my summer.五、what引导的主语从句与that不同的是,what除了可以引导主语从句起连接作用外,还同时在从句中充当主语或宾语。如:作主语:What really matters is that she needs a shower at once. (真正重要的是,她得马上冲个澡。)作宾语:What I am worried about is their taking my son to France. (我担心的是他们要把我儿子带到法国去。)有的时候,whatever也可以用来连接主语从句。如:Whatever you do makes no difference to me. (你做什么对我来说都没区别。)需要注意的是,当what或whatever引导主语从句时,一般不能改为由形式主语it来引导的句子。