____ is known to everyone that * is part of China.____ is known to everyone that * is part of China．A．As B．Which C．It D．What为何不选D?

选C，It
如果是D的话，What （is known to everyone that...）,后面应该有内容，因为括号里面的部分都是修饰What的，其实整个句子就是一个What，成分不全

What is known to everyone is that * is part of China.若选D要加个is

IT
==AS is nkown to everyone,* is part of China
== That * is part of China is known to everyone.
==* is part of China, which is known to everyone.
== What is known to everyone is that * is part of China
==*'s being part of China is known to everyone
== * is part of China, and that is known to everyone

如选D，应是
What is known to everyone is that * is part of China．=
It is known to everyone that * is part of China．=
As is known to everyone,* is part of China．
what 应引导主语从句，故需添加谓语is

选择C
当主语部分太长时为了句子平衡采用it作形式主语.所谓形式是指句子的真正主语将在句子末段出现.