What is the formula of past perfect continuous?

Related questions

1. What is the structure of past perfect continuous?
2. What is the rules of past perfect tense?
3. What is the rule of past perfect continuous?
4. What is the difference between past perfect and present perfect?
5. What is the past perfect of speak?
6. What is the difference between past and earlier past?
7. What is the rule of simple past?
8. Has stolen or stole?
9. What is the past of steal?
10. What is past perfect aspect?

Tags

1. #perfect
2. #still
3. #present
4. #formula
5. #subject
6. #happening
7. #progressive
8. #specific
9. #event
10. #participle
11. #continuing
12. #object
13. #about
14. #period
15. #formed
16. #continuous
17. #following