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. Her friends  had been thinking of calling the police when she walked in. (think)

2. They had been sleeping  for an hour before I went to bed. (sleep)

3. She had been playing  the trumpet for \(3\) years before she joined a band. (play)