Study some signal words for Past Perfect Continuous.
Words for Past Perfect Continuous:
for — в течение;
since — с, с какого-то момента;
when — когда;
how long — как долго;
before — до того.
In \(2014\) The Browns had been living in London for twenty years.
I had been working for Nike 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.
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.