It is such a difficult problem no one can work out. A. asB. thatC. soD. thus

问题补充：

It is such a difficult problem no one can work out.

A. as

B. that

C. so

D. thus

答案：

(答案→)A. as

B. that

C. so

D. thus

解析：such…as…“像这样的”，as 引导定语从句。