1/ sleeping ( HTTD ; dấu hiệu : right now )

2/ bought ( QKĐ ; dấu hiệu : yesterday ) - going to ( be going to )

3/ is attending ( HTTD ; dấu hiệu : at the moment )

4/ hasn't had ( HTHT ; dấu hiệu : for )

5/ starts ( HTĐ )

6/ have studied ( HTHT ; dấu hiệu : since )

7/ came ( QKTD )

8/ have done ( HTHT )

9/ am ( HTĐ )

10/ has waited ( HTHT ; dấu hiệu : for )

11/ called ( QKTD )

12/ was ( QKĐ )

13/ am talking ( HTTD ; dấu hiệu : at the moment )

14/ were ( QKĐ ; dấu hiệu : last year )

15/ rises ( HTĐ )

16/ met ( QKĐ ; dấu hiệu : yesterday )

17/ takes place ( HTĐ ; dấu hiệu : every four years )ư

18/ were playing ( QKTD ; dấu hiệu : a 4pm yesterday )

19/ was cooking ( QKTD )

20/ are playing ( HTTD ; dấu hiệu : now )

21/ saw ( QKTD )

1 sleeping

S + am/ is/ are+ Ving

2 bought

3 is attending

S + am/ is/ are+ Ving

4 hasn't had 

S + have/ has + V3

5 starts

6 have studied

S + have/ has + V3

7 came ( QKTD )

8 have done

S + have/ has + V3

9 am 

10 has waited 

S + have/ has + V3

11 called ( QKTD )

12 was 

13 am talking

S + am/ is/ are+ Ving

14 were  

15 rises 

16 met  

17 takes place  

18 were playing

S + was/were + Ving

19 was cooking

S + was/were + Ving

20 are playing 

S + am/ is/ are+ Ving

21 saw