Past perfect continues tense

The past perfect continues tense is used to express an action that was finished at a certain time in the past, but had been going on till that time;

E.g.

* Rama had been studying for two hours when I called him.

* We had been waiting for an hour when the bus arrived.
* You had been making a noise for a long time when the teacher stepped in.

Rule:- subject + had + been + root verb + ing

Examples:

* I had been suffering for a week when the doctor was called.
* He had been working in the field all day when the darkness fell.
* She had been cooking for two hours when the guests came.
* It had been raining for three hours when we set out.
* They had been selling goods when the police raided the shop.
* Harry had been vomiting all night when the day broke.
* Merry had been singing for an hour when she lost her voice.
* The patient had been suffering from toothache for many hours when the dentist extracted it.