由 had 加动词的过去分词构成。
例句：
She said she had never been to Paris. 她说她从未去过巴黎。
When the police arrived,the thieves had run away. 警察到达时，小偷们早就跑了。
By the time he was twelve,Edison had begun to make a living by himself. 到了十二岁那年，爱迪生开始自己谋生。