Study some signal words for Past Perfect Continuous.
Words for Past Perfect Continuous:
for — протягом;
since — з, з того часу;
when — коли;
how long — як довго;
before — до того.
In \(2014\) The Browns had been living in London for twenty years.

I had been working for this company since \(2017\).

We had been waiting for Mary since morning when she finally arrived at \(5\) pm.

They had been watching TV when the lights went off.
watch Tv.jpg

How long had you been waiting before he came?

James had been teaching at the university for more than a year before he left for London.