Question

________is known to all is that china has a larger population than any other country

A that B what C it D AS
答案是B 为什么 麻烦英语高手们解释解释 为什么不能选C 与D？

Answer 1

As is known to all,China has a larger population than any other country.(非限制性定语从句）
It is known to all that China has a larger population than any other country.（主语从句，it作形式主语）
What is known to all is that china has a larger population than any other country .（what引导的主语从句）
你比较一下这三个句子，就知道怎么选了。