the past perfect tense
by the time i got there, it had already finished.
when i got to the check-out, i realized i had left my purse at home.
he said he had never seen such an exciting match before.
when he had finished his work , he left his office .
after i had done my homework , i went to bed.
they had already had breakfast before they arrived at the hotel.
从句中"arrived at"到达在"过去"的时间，而"had already had"吃早饭的动作发生在到达之前，因此主句的时态为"过去的过去"。
i had finished writing my composition by 10:00 this morning. 今天上午10：00点以前，我已经写完了我的作文。
she had searched the internet for two hours when she found an ad for the canon digital camera. 当她找到了佳能数码照相机的广告时，她已经在因特网上查询了两个小时。
i went over what i had written again and again so that i wouldn't make any mistakes. 我一遍又一遍地检查了我所写的内容，以至我没有出现任何错误。
he remembered he hadn't paid for it yet. 他记得他还没有付账。
he said that he had never seen such a beautiful bird before.
how many english films had you seen by the end of last term?
had you reached the station before ten o'clock?