is known to us all, the earth is round.That is to say    is known to us all is that the earth is round .

1. A.
   As, what
2. B.
   As, as
3. C.
   what ,as
4. D.
   What ,what

        is known to us all, the earth is round.

That is to say     is known to us all is that the earth is round .

A. As, what     B. As, as      C. what ,as       D. What ,what