5. am, is, are - was,were - been
7. buy - bought - bought
8. drink - drank -drunk
9. clean - cleaned - cleaned
10. read - read -read
11. meet - met- met
12. take - took -taken
13. see - saw - seen
14. learn - learned - learned
learn - learnt - learnt
15. run - ran - run
16. eat - ate -eaten
17. find - found - found
18. understand - understood - understand
19. know - knew - known
20. come - came - come
Học tốt!!!