Explains an action which started in the past and continued for a considerable time
Ana had been living in this house for ten years
Positive sentence
subject + had been + v1st form + ing + object + for/since
I had been waiting for my friend for two days
Negative sentence
subject + had not been + v1st form + ing + object + for/since
She had not been reading for three hours
Interrogative sentence
had + subject + been + v1st form + ing + object + for/since
Had they been playing for many hours?