It had been snowing for 4 hours
Eton had been working for 20 years before he retired
Mike had been living there for a tonight
They had been studying German for 5 years before they went to Berlin
The authors had been working on the novel for 2 years before the sent it to a publisher
Pele had been playing football for 6 years before...
The students had been listening attentively to the dialog for an hour ...
The children had been walking for 2 hours..
(вместо точек просто продолжение предложения без изменений)