句子成分划分It is known to us how he became a writer.
问题描述：
句子成分划分It is known to us how he became a writer.
麻烦帮忙划分一下句子成分
答
It （形式主语）is known to us（谓语） how he became a writer（真正主语---主语从句）什么时候需要使用形式主语？但做主语的不定式，动名词或者主语从句放在句尾时，就必须用