Теория:

Study some information about positive sentences 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 утвердительного предложения нужно использовать следующий порядок слов:
subject \(+\) had \(+\) been \(+\) Ving \(+\) other parts of the sentence.
  
Examples
 
She had been working hard and managed to write this report on time.
 
              I                  
                                                               had been studying
 
       
            you
 
had been studying
 
he, she, it
 
had been studying
 
we
 
had been studying
 
You
 
had been studying
 
They
 
had been studying