请问新概念英语的这句话,是什么语法结构?新概念英语第三册第12课里有一句这样的话“perhaps there is an element of truth in both these picture,but few of us had an opportunity to find out”,这里为什么要用had an opportunity ,而不是have an opportunity.

问题描述:

请问新概念英语的这句话,是什么语法结构?
新概念英语第三册第12课里有一句这样的话“perhaps there is an element of truth in both these picture,but few of us had an opportunity to find out”,这里为什么要用had an opportunity ,而不是have an opportunity.