Este tempo verbal é usado para indicar uma ação em progresso antes de um momento específico no passado. Algo que teve início no passado e continuou até o momento em que outro evento ocorreu.
I had been working hard for 10 years before I got that promotion.
She had been studying for 6 years before she became a lawyer.
O Past Perfect Continuous pode ser usado também para expressar a idéia de causa e efeito, sempre se referindo a eventos no passado.
He became so muscular because he had been doing lots of exercises.
She got the best marks because she had been only studying.
Se não especificamos a duração de um evento, podemos usar o Past Continuous, desde que a idéia a ser expressar for de interrupção.
I was sleeping when the door bell rang. => I woke up when I heard the door bell.
I had been sleeping for 2 hours when the door bell rang. => I slept for 2 hours, woke up just before the bell rang.
Existem algumas expressões indicadoras deste tempo verbal, sendo as mais comuns: when, before, prior to, until.
Para formar sentenças no Past Perfect Continuous, usamos as regras:
Afirmativa: had been + verbo principal no gerúndio. had been verbing
I had been working for the same company until I finally quit.
She had been waiting for more than one hour when you arrived.
Negativa: Adicione “not” depois do primeiro verbo auxiliar. had not been verbing
He had not been gambling until you invited him.
Interrogativa: Inverta o sujeito e o primeiro verbo auxiliar.
What had you been doing when his grandmother called?