This is so difficult a problem as no one can work out.as能不能换成which 为什么

This is so difficult a problem as no one can work out.as能不能换成which 为什么

可以,但意思会有变化
This is so difficult a problem as no one can work out.这个问题很难,因为没人能解决.
This is so difficult a problem which no one can work out.这是个没人能解决的难问题.

so...as 固定搭配 太。。。以至于。。。

可以的 which引导非限制性定语从句