英语：The book was so interesting that he had read it for three hours____he realized it.

题目

英语：The book was so interesting that he had read it for three hours____he realized it.
为什么是before?解释下意思and语法知识.

答案

had read it是过去的过去 是过去完成时 后者he realized it是一般过去时 用before表示先后 而and则表示并列 两边时态要一致