过去完成时常用的时间状语有
1. by the end of last+时间段. By the end of last term, we had learned 5000 new words.
到上学期末,我们已经学了5000个新词。
2. By the time sb. +动词过去式如:The bus had already left by the time I got there.
3.By (the time of)+时间段
By the time of last year ,we had built two bridges.