Question

___ is known to everybody,Taiwan is a part of China.We must unify it.

A.It B.as
请问为什么？
为什么A不可以？

Answer 1

as is known to sb,意思是”某人知道。这个地方可以翻译成：每个人都知道..
it is known that是固定结构。。。意思和刚才的一样：每个人都知道..
其实选择it 的话 ，也可以 ，但是呢，要去掉那个逗号，或者说把逗号改成that，那么这样的话就是
it is known to everybody that Taiwan is a part of China.We must unify it.

Answer 2

As.
这种格式在一些书上称作“定语从句”，由as引导，可放在前边也可放在后边。也有人认为是状语从句。不过意思都是一样的：正如人人知道的那样。
It 需要完整的结构，也就是It is known to everybody that Taiwan ....

Answer 3

B。
As is known to everybody是非限制性定语从句+主句Taiwan is...

Answer 4

选择B,固定用法。