31. will have 

32. to tell 

33. will be built

34. won't go

35. will be cycling

36. was / smoke

37. use

38. did you go / went

39. did not use

40. are you doing / am watching

41. will be lying

42. to smoke

43. hasn’t come

44. are

45. goes

46. seeing

47. has learnt

48. watched

49. use

50. is

$\text{31. will have (S + think + will + V(b) + O)}$

$\text{32. to tell (used to + V(b): diễn tả thói quen trong QK bây h ko còn)}$

$\text{33. will be built ( Câu bị động thì tương lai đơn)}$

$\text{34. didn't go .......... was (last Sunday ⇒ Thì QKĐ)}$

$\text{35. will be cycling (at 6.30 tomorrow ⇒ Thì TLTD)}$

$\text{36. was ......... to smoke (When QKĐ, QKĐ - used to + V(b): diễn tả thói quen trong QK bây h ko còn)}$

$\text{37. did ...... use (used to + V(b) : giải thích trên)}$

$\text{38. did you do ............ went (last night ⇒ Thì QKĐ)}$

$\text{39. didn't use (in the evening last month ⇒ used to (mỗi tối tháng trước)}$

$\text{40. are you doing ........ am watching (at the moment ⇒ Thì HTTD)}$

$\text{41. will be lying (next week at this time ⇒ Thì TLTD)}$

$\text{42. smoke (must/ must not + V(b)}$

$\text{43. hasn't come (for a long time ⇒ Thì HTHT)}$

$\text{44. are (there ..... two hospitals ⇒ are (số nhiều)}$

$\text{45. goes (usually ⇒ Thì HTĐ có chủ ngữ số ít ⇒ V(s/es)}$

$\text{46. seeing (How about + V-ing + ........?}$

$\text{47. has learnt (for 8 years ⇒ Thì HTHT)}$

$\text{48. watched (last night ⇒ THÌ QKĐ)}$

$\text{49. will be use (Đèn sử dụng ít năng lượng sẽ được dùng trong tương lai)}$

$\text{50. will be (S + think + will + V(b)}$