$\text{13.}$ visited

$\text{→}$ last ⇒ QKD

$\text{14.}$ have you waited

$\text{→}$ How long + have/ has + S + PP?

$\text{15.}$ says

$\text{→}$ often ⇒ HTD

$\text{16.}$ didn't go

$\text{17.}$ is singing

$\text{→}$ listen! ⇒ HTTD

$\text{18.}$ cut

$\text{19.}$ don't eat

$\text{20.}$ returned

$\text{→}$ yesterdy ⇒ QKD

$\text{21.}$ is coming

$\text{→}$ Hurry up! ⇒ HTTD

$\text{22.}$ am having

$\text{→}$ now ⇒ HTTD

$\text{23.}$ have you studied 

$\text{24.}$ haven't seen

$\text{→}$ for ⇒ HTHT

$\text{25.}$ did you do - did

13. visited (dấu hiệu last summer chia QKĐ)

14. have you waited (dấu hiệu how long chia HTHT)

15. says (dấu hiệu often chia HTĐ)

16. didn't go (dấu hiệu last Sunday chia QKĐ)

17. is singing (dấu hiệu Listen! chia HTTD)

18. cuts (không có dấu hiệu cụ thể chia HTĐ)

19. don't eat (một hoạt động có tính quy luật của một vài động vật)

20. returned (dấu hiệu yesterday chia QKĐ)

21. is coming (dấu hiệu Hurry up! chia HTTD)

22. am having (dấu hiệu now chia HTTD)

23. have you studied (dấu hiệu how long chia HTHT)

24. haven't seen (dấu hiệu for+khoảng thời gian chia HTHT)

25. did you do... did (dấu hiệu last night chia QKĐ)