Question

________ is all known to all, water is ________ hydrogen and oxygen．

1. A.
   As; making
2. B.
   It; made up of
3. C.
   As; composed of
4. D.
   Which; consisted of

Answer 1

C
As is known to all是一个定语从句，并不是It is known to all that…结构。which引导的定语从句不能放在句首。be composed of, be made up of和consist of均意为“由……组成”。