What is the past perfect continuous?

Related questions

1. What is rule of present perfect continuous tense?
2. When we use future perfect continuous tense?
3. What is the difference between present perfect and present perfect continuous?
4. What is the present perfect tense of teach?
5. When use the present perfect continuous?
6. What are present perfect tense examples?
7. Where present perfect tense is used?
8. What are perfect tenses in English?
9. What's the difference between past perfect and past perfect continuous?
10. What is the structure of the present perfect continuous tense?

Tags

1. #until
2. #action
3. #present
4. #constructed
5. #participle
6. #tense
7. #continuous
8. #using
9. #continued
10. #known
11. #shows
12. #started
13. #another
14. #perfect
15. #progressive