we found this problem difficult to solve solve为什么不用被动

问题描述:

we found this problem difficult to solve solve为什么不用被动

difficult to do ,习惯用法.不需要被动态.
有点类似中文里说:“我们发现这个问题难以解决”而不必严格地说:“我们发现这个问题难以被解决”.