Question

什么是主语从句?怎么用?

Answer 1

作句子主语的从句叫主语从句.主语从句通常由从属连词that,whether,if和连接代词what,who,which,whatever,whoever以及连接副词how,when,where,why等词引导.that在句中无词义,只起连接作用；连接代词和连接副词在句中既保留自己的疑问含义、又起连接作用,在从句中充当从句的成分.例如：
What he wants to tell us is not clear.他要跟我们说什么,还不清楚.
Who will win the match is still unknown.谁能赢得这场比赛还不得而知.
It is known to us how he became a writer.我们都知道他是如何成为一名作家的.
Where the English evening will be held has not yet been announced.英语晚会将在哪里举行,还没有宣布.
有时为避免句子头重脚轻,常用形式主语it代替主语从句作形式主语放于句首,而把主语从句置于句末.主语从句后的谓语动词一般用单数形式.常用句型如下：
（1） It + be + 名词 + that从句
（2）It + be + 形容词 + that从句
（3）It + be + 动词的过去分词 + that从句
（4）It + 不及物动词 + that 从句
另注意在主语从句中用来表示惊奇、不相信、惋惜、理应如此等语气时,谓语动词要用虚拟语气“(should) +do”,常用的句型有：
It is necessary (important,natural,strange,etc.) that …
It is a pity (a shame,no wonder,etc.) that…
It is suggested (requested,proposed,desired,etc.) that…