1. Lan is my sister. (be)
2. They are my cousins. (be)
3. I am not good at Math. (not be)
4. Are you a teacher?
5. Is he a good student?
6. Is it a pen?
7. My friends isn't friendly. (not be)
8. I and Mai are friends. (be)
9. It isn't a table. (not be)
10. We are students of Yen Vien Secondary School.
11. How old are you? (be)
12. How old is she? (be)
13. Who are they? (be)
14. This is a book and these are pens. (be)
15. Are you in class 4A? (be)
16. There are many flowers in my garden. (be)
17. There aren't any flowers in my garden. (not be)
18. Are there any flowers in your garden? (be)
19. I am not a student in class 5C. (not be)
20. What time is it? (be)