Let's explore each in detail:

1. Present Perfect Continuous Tense:

   • Formation: Subject + "have/has been" + present participle (-ing form) of the main verb.
   • Usage: Describes actions or states that started in the past, continue in the present, and may continue into the future. It emphasizes the ongoing nature of the action or state.
   • Example:
     • She has been studying for three hours.
     • They have been playing basketball since morning.
     • We have been waiting for the bus for half an hour.

2. Past Perfect Continuous Tense:

   • Formation: Subject + "had been" + present participle (-ing form) of the main verb.
   • Usage: Describes actions or states that were ongoing in the past before another past action or a specific point in the past. It indicates the continuity leading up to a specific time in the past.
   • Example:
     • I had been working on the project all day before I took a break.
     • They had been traveling for weeks before they reached their destination.
     • She had been practicing the piano for hours before the performance.

3. Future Perfect Continuous Tense:

   • Formation: Subject + "will have been" + present participle (-ing form) of the main verb.
   • Usage: Describes actions or states that will be ongoing and in progress before a specific future time or reference point. It emphasizes the continuity leading up to a future moment.
   • Example:
     • By next month, she will have been studying English for a year.
     • They will have been working on the assignment for days by the time it is due.
     • We will have been waiting at the airport for hours before the flight arrives.

Key Points to Remember:

• Perfect continuous tenses indicate ongoing or continuous actions or states that started in the past and continue to a specific point in time.
• They are formed using an auxiliary verb (have/has been, had been, will have been) followed by the present participle (-ing form) of the main verb.
• The time frame of the action determines the tense used (present, past, or future).
• Perfect continuous tenses often include time expressions to specify the duration or timing of the action or state.
• These tenses are particularly useful for discussing ongoing activities, durations, or states that have relevance in relation to specific timeframes.

By understanding the perfect continuous tenses, you can effectively convey ongoing actions, states, or durations in relation to past, present, or future timeframes.