My friend hasn't bought any books for a year

It's a year since my friend last bought books

The last time my friend bought books was a year ago

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

`=>` It's + time + since + S + last + V2/ed 

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

`EKI2k7`

`-` It is a year since my friend last bought some books.

`-` The last time my friends bought some books was a year ago.

`-` My friend last bought some books a year ago.

`××××××××××××`

`-` S + hasn't/haven't + P2 + since/for...

`=` It is + thời gian + since + S + (last) + Ved

`=` The last time + S + Ved + was + thời gian + ago

`=` S + last + Ved + thời gian + ago.