rewrite sentences with the same meaning.

`16.` It's `10` years since they lived here.

`->` S + have/has + P2 + for + time

`=` It's + time + since + S + Ved/V2

`17.` This is the first time I have read a detective story.

`->` S + have/has + never + P2 + before

`=` This is th first time + S + have/has + P2

`18.` I have not seen him since I was a student.

`->` S + last + Ved/V2 + when + S + was/were + adj/N

`=` S + have/has not + P2 + since + S + was/were + adj/N

Các công thức đổi HTHT - QKĐ

Type 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 

Type 2:

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

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

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

Type 3: 

S + has/have + not/never + V3/ed + ... before

--> This/It is the first time + S+ has/have+ V3/ed

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16. It's ten years since they lived here.

17. This is the first time I have ever read a detective story.

18. I have not seen him since I was a student.

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