Simone
到最近或过去的某个时间点一直在进行的事情可以用过去完成进行时，到过去的某个时间乎猛点已经完成的事情用过去完成时。例：
例：I'd been finishing some work in the garden when Lea arrived, so I didn't hear her come in. （Lea到的时候我正在工作收尾，活儿还没干完，所以要用过去完成进行时，不能用过去完成时I'd finished...）
有些情况下过去完成进行时和过去完成时的意思是相同的，可以互换。
例： I'd been working/I'd worked hard all year, so I felt that I deserved a holiday.
一直到过去的某个时间点前的一段时期内重复发生的行为，用过去完成时而不是过去完成进行时。
例：I had stayed in the hotel twice in the 1990s. （不能用I had been staying in the hotel twice...）
过去完成进行时可以用来讲述过去某个时间点前持续发生的情况或进行的行为，并且是以下三种情况之一：a)到该时间岁物桥点完成，b) 继续进行，c)该时间点不久前完成。
例：We'蚂烂d been driving for about an hour when the engine suddenly stopped.
如果对行为持续的时长不感兴趣，则可以用过去进行时替代过去完成进行时。
例：A friend told me about a conversation she'd recently overheard. Two women were discussing their holiday plans...（朋友听到了两个女人在讨论假日计划，讨论了多久并不重要）
英语里面不会用任何进行时态描述一种状态，即使强调状态持续的时间，也要用过去完成时而非过去完成进行时
例：We had only owned the car for six weeks when the clutch broke. （不能用We had been owning the car for six weeks.）
过去完成进行时多见于书面，口语里很少用到。
例：Carl Sims had been climbing alone near the Harz Waterfall, which has claimed many lives in the past.
