[had + past participle]
- She had learnt Japanese before she moved to Japan.
- Had he seen his uncle when he came back?
- By 1970,he hadn't graduated from the niversity.
The past perfect expresses an activity that was completed before another activity or time in the past.
- She had cleaned the house before her husband came back.
- By the time he was 42,he had taught for 20 years.
- As soon as he had graduated from university,he got employed in a company.
- They were arrested because they had demonstrated in the street.
- She wishes she hadn't been divorced.
- After her neighbour raped her,she suicided.
Had been +verb+ing.
The past perfect progressive emphasizes the duration of an activity that was in progress before another activity or time in the past.
- She had been learning computation theories for seven years before she invented that software..
- Had his wife been accompanying him through the cheering crowds?
- he had been killing ruthlessly his political oponents for years without qualm.