Past Perfect Continuous

USES:
- To talk about something that started in the past and continued up until another time in the past.
- Before another action in the past, to show cause and effect.

FORM:

- AFFIRMATIVE: Had been + Verb -ing    
I had been playing basketball.       

- NEGATIVE: Had not been + Verb -ing            
I hadn't been playing football.         

- QUESTION: Had + Subject +  Been + Verb -ing + Complements?  
Had you been playing tennis?      

HAD is the auxiliary verb.

Links to exercises:

Past perfect continuous 1