13.______ is known to the world,Mark Twain is a great American writer.

问题描述:

13.______ is known to the world,Mark Twain is a great American writer.
A.It
B.As
C.Which
D.That

B
As 引导非限制性定语从句,代替整个主句Mark Twain is a great American writer
which 引导的非限制性定语从句不能放在主句前