When we choose A,we should put a comma after the word "all",
When we choose B,it is lacking of a conjunction "that"
C is a useful pattern.It is known to us all=People know
When we choose D,we also have a comma after the word"use"
Ok,this is done by me------an English teacher
The following are correct.
As is known to all,the
As we all know,the
It is known to all that the.
Is it clear?
My qq number is 136140008 and you can contact me.