is known to all paper was first made in China.A. ItB. ThatC. WhichD. As

问题补充：

is known to all, paper was first made in China.

A. It

B. That

C. Which

D. As

答案：

A. It

B. That

C. Which

(答案→)D. As

解析：由逗号可知,前面是一个非限制性定语从句,所以用As；Which引导定语从句不可置于句首；若把逗号改为that,则成为主语从句,答案则选A.