過去完成時典型例題
　　
The students ___ busily when Miss Brown went to get a book she ___ in the office.　
A. had written, left　B，were writing, has left C. had written, had left　D. were writing, had left
　　
答案D. "把書忘在辦公室"發(fā)生在"去取書"這一過去的動作之前，因此"忘了書"這一動作發(fā)生在過去的過去，用過去完成時。句中when表示的是時間的一點，表示在"同學(xué)們正忙于……"這一背景下，when所引導(dǎo)的動作發(fā)生。因此
　　
前一句應(yīng)用過去進行時。
注意：　had no … when　　　　　還沒等…… 就……
had no sooner… than　　剛…… 就……
He had no sooner bought the car than he sold it.