主语从句：在句中作主语的名词性从句称为主语从句,主语从句所对应的谓语动词通常用第三人称单数的形式.为了整个句子的平衡,主语从句经常后置,并用it充当形式主语(此时,that引导的主语从句若不放在句首,可以省略引导词that).例如：What she did is not yet known.她干了什么尚不清楚.// Whoever comes is welcome.不论谁来都欢迎.// It is a pity (that) we haven’t contacted for ages.很遗憾,我们几年没联系了.// It has not been decided where the meeting is to be held.在哪里开会还没决定.// It doesn’t matter whether she will come or not.她是否来这无关紧要.
注意：不要混淆it 作形式主语指代主语从句与it引导强调句型的情况：
it作形式主语代替主语从句主要是为了平衡句子结构,主语从句的连接词没有变化； it引导的强调句则是对句子某一部分进行强调,无论强调的是什么成分,都可用连词that(被强调部分指人时也可用who/whom) // 区分it 作形式主语指代主语从句与it引导强调句型的有效技巧是：将“It be ...that ...”中的it be和that去掉后,句子仍然成立的是强调句,句子不能成立的是that引导的主语从句.例如：It was my suggestion that made him confident of success.正是我的建议使他对成功有了自信.去掉it be和that后可以构成完整的强调句型的原型“My suggestion made him confident of success.”,因此本句属于强调句.
It is my suggestion that he needs more practice.他需要更多的练习是我的建议.去掉it be和that后本句讲不通,因此本句属于主语从句.
It appears to me that he may play an important role in setting the problem.It appears to me that接从句.It appears to me接主语从句.
It seems that no one knew what had happened.It seems that接主语从句.
以上回答供您参考!希望对您有所帮助!
杭州图书馆