The story was so interesting that she had read it for three hours ___ she realized it.

问题描述:

The story was so interesting that she had read it for three hours ___ she realized it.
A.when B.before C.after D.until
为什么不选A呢?

就是B 这是一个完成时态的句子.had done sth before sb did,在某人还没有来得及做某事之前就已经.意思是在他还没有意识到之前,他已经读了三个小时了