1. When I had got downstairs the phone stopped ringing.
2. I was sorry to leave, as I had enjoyed the party very much.
3. Helen was very upset because she lost her purse.
4. It had been a very difficult day, so I had went to bed early.
5. When I turned on the TV, the match had finished.
6. We didn’t get a table in the restaurant because we hadn't booked.
выбор в времени в этих предложениях зависит от смысла past perfect используется для "предпрошедшего" действия. например в 5: когда я включил телик, матч уже закончился = сначала матч закончился (past perfect), а потом я включил телик (past simple) Good lick!