ЕГЭ/Английский язык/Past Perfect Progressive

Past Perfect Progressive' образуется при помощи
глагола to be в Past Perfect + Participle 1 (had been doing).

Nota Bene:

Participle I это форма глагола с окончанием на -ing (going, seaching, watching ...)

Past Perfect Progressive может обозначать действие, которое завершилось
перед другим действием в прошлом и имело определенную длительность.

- Although the sun was shining, it was still cold as it had been raining hard for two hours.

- He felt tired when he came home as he had been playing football.

Past Perfect Progressive также употребляется, чтобы показать,
как долго что-либо происходило перед тем, как что-то еще случилось.

- She had been sleeping for two hours when we returned. - It had been raining for an hour when I left home.

The following is worth thinking over!
Past Perfect Progressive (had been doing)- это прошедшее время от Present Perfect Progressive
(have been doing).

Present Past

How long have you been waiting?(до сих пор)He's out of breath. He has been running.

Past How long had you been waiting when the bus finally came?
He was out of breath. He had been running.

Past Perfect Progrssive (had been doing) и Past Progressive (was/were doing):

She had been sleeping for three hours when we returned.

(есть есть указание на то, как долго продолжалось действие).

She was sleeping when we returned.

(нет указания на то, как долго продолжалось действие).