he was about to chang his mind when an idea_to him

问题描述:

he was about to chang his mind when an idea_to him
a occurred b had occured
c was occured d had been occured

选 A
这里occure发生,和happen一样,是没有被动语态的,所以排除C和D
when引导的时间状语从句,时态必须一致,主句用过去时,从句也用过去时.