The past perfect progressive tense describes an activity that was ongoing up until another point in the past. It is formed using "had" plus the present participle of the verb (ending in "-ing"). This tense emphasizes the duration of an activity leading up to another past event or time. Examples given were "The police had been looking for the criminal for two years before they caught him" and "We had been waiting for Nancy for over three hours before she finally arrived yesterday."

1. Past Perfect Progressive Present Past Future

2. Past Perfect Progressive Form : had + Been + present participle ( -ing form of the V. ) Present Past Future

5. Thank You!