Past perfect progressive tense indicates an ongoing event that was completed in the past, prior to some other past event.
- We had been looking for a house for six months when we found this one.
- Mark had been applying for other jobs before he was laid off.
The pattern for forming past perfect progressive tense is as follows:
- Had + been + present participle
To form the negative, place not between had and been. To form a question, move had to the beginning of the sentence, in front of the subject.
- We had been looking for a house.
- Had we been looking for a house?
- We had not been looking for a house.