PAST PERFECT CONTINUES:
PAST PERFECT CONTINUES to say how long something
had been happening before something else happened :
For Example : S + Had + Been + V1 ing
->1. The soccer game had to be stopped.
They had been playing for half an hour when there were a terrible storm.
->2. Ken had been smoking for 30 years when he finally gave it up.
COMPARE : no.1 and no. 2
->1. When I look out the window, it had been raining. ( It was not raining when I looked out. )
->2. When I look out the window, it was raining. ( Rain was falling at the time I looked out. )
=>>COMPARE : no.1 and no. 2=>>
Present Perfect >< Past Perfect
->1. How long have you been waiting ? ( until now ) –
>2. How long had you been waiting when the bus finally came?
->1. He is out of breath. He has been running.
->2. He was out of breath. He had been running.