你好,这个句子是由主语从句转换来的 1) 在主语从句中, 为了防止句子头重脚轻,通常把形式主语it放在句首位置,真正主语搁置于句末 用it 作形式主语的结构 (1) It is +名词+that从句 It is a fact that … 事实是… It is an honor that …非常荣幸 It is common knowledge that …是常识 (2) it is +形容词+that从句 It is natural that… 很自然… It is strange that… 奇怪的是… (3) it +不及物动词+that从句 It seems that… 似乎… It happened that… 碰巧… (4) it is+过去分词+that从句 It is reported that… 据报道… It has been proved that… 已证实… 2)常规主语从句,即句子在复合句中充当一个主语 3)主语从句的时态:不受主句的时态影响和限制。 如:It is important that we all should attend the meeting. 其实就是 that we all should attend the meeting is important 具体可以参考 http://baike.baidu.com/view/100914.htm 希望帮到你