`12` Samuel has kept a diary since `1997`.

`13` I have lived in Ho Chi Minh City since I was `8`.

`14` She started teaching the children in this remote village five months ago.

`15` We have learned English for five years.

`16` They haven't talked to each other for two months.

`17` She hasn't seen her elder sister since `1999`.

`-----`

`***`

`-` S + started/began + Ving + since + thời gian/thời gian + ago

`=` S + have/has + V3/ed + for + thời gian/since + S + V2/ed

`-` S + last + V2/ed + thời gian + ago

`=` The last time + S + V2/ed + was + thời gian + ago

`=` S + have/has + not + V3/ed + for + thời gian

Các công thức đổi HTHT - QKĐ

Structure 1: 

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 

Structure 2: 

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

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

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

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12. Samuel has kept a diary since 1997.

13. I have lived in Ho Chi Minh City since I was 8.

14. She started teaching the children in this remote village five months ago.

15. We have learnt English for five years.

16. They haven't talked to each other for two months.

17. She hasn't seen her elder sister since 1999.

`color{orange}{~MiaMB~}`