It was October 1st, 1949 when the People's Republic of China was founded.
解答:这句子其实是含有关系副词when引导的定语从句,不是状语从句。
it是人称代词,表示时间,句子的意思是:那是1949年10月1日,那天中华人民共和国建立了。
延伸比较理解:
It was (on)October 1st, 1949 (that) the People's Republic of China was founded.
这是强调句了。其判断办法是:去掉it be...that...句子结构仍然完整。
句子意思:中华人民共和国是在1949年10月1日建立的。
it引导的主语从句:
That he is a great scientist is known .
That he is a great scientist是一个主语从句,在句首,句子“头重脚轻”,所以用it作形式主语了,可以改成:It is known that he is a great scientist.
追问怎么会是定语从句呢,又不是起修饰作用
追答定语从句,修饰先行词October 1st, 1949