在时间状语从句中的运用：
例如一些引导词 since, until, no sooner...than, hardly...when, scarcely...when 等，一般可视为 "had done" 出现的信号,从句常用一般过去时。
No sooner had Whitney Houston began to sing a song than there was an instant sensation.
惠特妮·休斯顿一开始唱歌，就引起了瞬时的轰动。（注意：这里由于no sooner 否定前置，句子谓语部分倒装，所以”had”提前）
It was a long time since Darcy had lived in this city.
达西住在这座城市已经有很长时间了。（达西在过去的某个时间点之前就住在这座城市）
