Теория:

Study some information about questions (general and special) in Past Perfect Continuous.
 
Для образования Past Perfect Continuous необходимо использовать структуру had been и основной глагол с окончанием -ing.
Subject \(+\) had \(+\) been \(+\) Ving \(+\) other parts of the sentence.
Для построения вопросительных предложений нужно использовать следующий порядок слов.
 
General question
Had \(+\) subject \(+\) been \(+\) Ving \(+\) other parts of the sentence?
Had she been cooking a lemon pie for an hour before I came?
 
pie-1514111_640.png
Рис. \(1\). Lemon pie
 
Special question
Question word (when, why, how, what...) \(+\) had \(+\) subject \(+\) been \(+\) Ving \(+\) other parts of the sentence?
Why had he been talking on the phone for half an hour when I entered the room?
 
man-3469587_640.png
Рис. \(2\). Talking on the phone
 
Источники:
Рис. 1. Lemon pie, 2016, https://pixabay.com/images/id-1514111/ Pixabay License CC0 Free for commercial use No attribution required
Рис. 2. Talking on the phone, 2016, https://pixabay.com/images/id-3469587/ Pixabay License CC0 Free for commercial use No attribution required