What Had Been Happening Before Something Occurred
Past Perfect Continuous
The past perfect continuous expresses the duration of an activity up to another point in time in the past. The use of the past perfect continuous stresses that a certain activity had been going on before something important happened.
Example:
The economy had been struggling through a bear market for so long that people didn't know how to react.
How often had you been checking your safety deposit box prior to the break-in?
They had been explaining the fixed exchange rate when the officer entered the hall.
Positive Form:
Subject + had + been + 'ing' form of verb + (object(s)) + time expression
She had been working on the fixed exchange rate report for five hours when he asked for it.
Negative Form:
Subject + had + not + been + 'ing' form of verb + (object(s)) + time expression
They hadn't been using that credit card account long when they used up their card's limit.
Question Form:
(Question Word) + had + subject + been + 'ing' form of verb?
How often had you been checking your safety deposit box prior to the break-in?
Past Perfect Contrasted with Past Perfect Continuous
The past perfect expresses something that finishes before another activity in the past. The past perfect continuous, on the other hand, expresses the duration of an activity at the moment something important happened in the past.
Past Perfect Examples:
She hadn't had time to act on behalf of Jim before she made the presentation.
He hadn't kept his account for long before it was cancelled.
Past Perfect Continuous Examples:
The economy had been struggling through a bear market for so long that people didn't know how to react.
How often had you been checking your safety deposit box prior to the break-in?