At that time we
(我们那时已经在台北住了十年了。) – situation which continued up to the past moment that we are talking about
When I found Mary, I could see that she had
(我找到玛莉时，我看得出来她刚哭过。) – action which stoped shortly before the past moment that we are talking about
◎ 表示过去的持续行为 (藉此表达“原因和理由”)
John was tired because he had been jogging.
John was tired because he was jogging.
Sam gained weight because he had been overeating.
(Sam 那时变胖了，因为他都 (一直) 饮食过量。)
Kathy failed the final examine because she had not been attending class.
(Kathy 那时 (一直) 都没上课，所以期末考不及格。)
I could smell that he had been smoking.
◎ 过去完成式 vs 过去完成进行式的
My leg was stiff because I had been standing still for a long time. (Practical English Usage by Michael Swan, p 421 )
(我当时站着不动很久，腿都僵硬了。) – 强调“持续”
The lived in a castle which had stood on a hill for 200 .
(他们居住在山丘上一座有两百年歷史的城堡。) – 强调“永久”
I had been reading science fiction for years when I bought my first computer.
(我那时买第一部电脑时，已经读了十年科幻小说。) – 强调“持续”
I had read all my magazines, and was beginning to get bored. (Practical English Usage by Michael Swan, p 421 )
(我当时已经读完我的全部杂誌，开始感到无聊。) – 强调“完成”
例如：know / belong
The car had been belonging to my elder brother for years before I bought it. (错误)
The car had belonged to my elder brother for years before I bought it. (正确)
Jason hadn’t known Kathy for very long when he propsed to her.
(Jason hadn’t been knowing Kathy…)