49. Susan may know the address.

`-` S + may + V_inf : Ai có thể làm gì

50. He has learned English since he was in grade 6

`-` HTHT : (`+`) S + have/has + V3/ed 

51. I last visited the museum three months ago.

`-` S + last + V2/ed + time + ago : Ai lần cuối làm gì

52. His mother has uploaded his cover song videos on social media since yesterday.

`-` HTHT : (`+`) S + have/has + V3/ed 

53. My mother started doing the laundry ten years ago.

`-` S + start + V_ing : Ai bắt đầu làm gì

54. People must work here and leave by by 6 p.m

`-` S + must + V_inf : Ai phải làm gì 

49. Susan may know the address.

may + V1: có thể …

50. He has learnt English since he was in grade 6.

S + has/have + V3/ed + for/since + time 

--> S + started / began + to V / Ving 

--> It is / has been + time + since + S+ V2/ed

51. I last visited the museum three months ago.

S + has/have + not + V3/ed + for/since + time 

--> S + last + V2/ed 

--> The last time + S+ V2/ed + was + time 

--> It is / has been + time + since + S+ (last) + V2/ed 

52. His mother has uploaded his cover song videos on social media since yesterday.

53. My mother started to do the laundry ten years ago.

54. People must work here and leave by 6 p.m.

must + V1: phải làm gì (mang tính bắt buộc)

`color{orange}{~LeAiFuRuiHuiBao~}`