16. is having=> was having

S+ Vqkđ while+ S+ was/were+ Ving

17. are=> have been

for=> htht: S+ have/has+ P2

18. are believing=> believe

htđ: S+ Vs/es

19. had been=> has been

recently => htht: S+ have/has+ P2

20. waking=> wakes

every =>htđ: S+ Vs/es

21. drives=> was driving 

S+ Vqkđ while+ S+ was/were+ Ving

22. will certainly complete => will have certainly completed

By the time + S + Vs/es , S + will + have + Ved/V3

23. buys=> bought

Vhtht+ since+ S+ Vqkđ

24. We'll be cycled=> we will have cycled

at this time next sunday=> tlht: S + will + have + Ved/V3

25. won't come=> don't come

S+ will V+ when+ S+ Vhtđ

26. was knocking=> knocked

S+ Vqkđ when+ S+ was/were+ Ving

27. didn't drink=> hasn't drunk

Vhtht+ since+ S+ Vqkđ

28. when=> since

Vhtht+ since+ S+ Vqkđ

29. gone=> going

tlg: S+ tobe+ going to V

30. did=> will

next=> tlđ: will+ S+ V?