________ was known to all, perseverance is a kind of quality and that's ________ it takes to do anything well．

1. A.
   As; which
2. B.
   As; what
3. C.
   It; which
4. D.
   It; what

_______ was known to all, perseverance is a kind of quality and that’s ______ it takes to do anything well．

A．As; which                    B．As; what

C．It; which                                D．It; what