I had been doing my homework for two hours when my mother came.
We had been driving a car for three hours before our car broke down.
Tom had been watching the film for 2 hours when the
TV screen suddenly went blank.
She had not been sleeping for a night before we returned.
Why had you been waiting for us since 5 o'clock before we came?Who had been discussing this problem for an hour when we came?He had been playing computer games for three hours when we came.What had they been doing for an hour before we came?The pupils had been writing a test for two hours before the bell rang.