Read these sentences and fill in the gaps with the correct verb form in the past perfect continuous.
Example 0. John __________ his dog all day. He was tired yesterday. (walk)
Answer 0. had been walking.
1. We to open the door for five minutes when Jane found her key. (try)
2. They for an hour before I went to bed. (sleep)
3. She the trumpet for \(3\) years before she joined a band. (play)