A.過去完成時和過去完成進行時
過去完成時：I had taken a bus into town.
過去完成進行時: I had been swimming in the pool
B.形式
positive form: I had been waiting ages.
negative: I had not been waiting ages.
question: had it been raining?
C.I had been doing or I had done?
had been doing:持續一段時間，通常接時長短語，通常不用於表示狀態 When the company went bankrupt ,it had been losing money for months.
had done：已經完成，通常接量詞短語，可以擁有表示狀態 When the company went bankrupt,it had lost over a million pounds.
D.同其他時態比較
現在完成時和過去完成進行時
Vicky looks very upset.I think she's been crying.
Vicky looked very upset.I shought shed'd been crying.
過去進行時和過去完成進行時
When I phoned,Natasha was having a piano lesson.
When I phoend,Natasha had been having a piano lesson.