分类：教育/科学-外语学习
问题：高二英语单选helen________herkeysintheo 
helen________her ys in the office,so she had to wait until her husband___________homea had left,comesb left ,had comec had left,camed had left,would come为什么选择C?为什么完成式用在前面而后面部用呢？如果完成式放在后边，过去式放在前面行么？为什么
回答：

从句是过去式，主句的动作发生在重句前，因此用过去完成式。