Tenses Questions
The past perfect tense is used to indicate an action that was completed before another past action or time. It is formed by using the auxiliary verb "had" followed by the past participle of the main verb.
Example: She had already finished her homework before her friends arrived.
On the other hand, the past perfect continuous tense is used to indicate a continuous action that started in the past and continued up until another past action or time. It is formed by using the auxiliary verb "had been" followed by the present participle of the main verb.
Example: They had been playing tennis for two hours when it started raining.
In summary, the main difference between the past perfect and past perfect continuous tenses is that the past perfect focuses on the completion of an action before another past event, while the past perfect continuous focuses on the duration of a continuous action before another past event.