`1)` I haven't had my hair cut since I left her.

`->` S + have/has (not) + V3 + since V-ed ... ai (chưa) làm gì kể từ khi ...

`2)` She hasn't kissed me for `5` months.

`->` S + have/has (not) + V3 + for [time]: ai chưa làm gì trong bao lâu

`->` she là số ít `=>` has

`3)` The last time I saw him was `8` days ago.

`->` The last time + S + V-ed + was/were [time] + ago: lần cuối ai làm gì là khi nào

`->` the last time là số ít `=>` was

`4)` She hasn't met her parents for `3` months.

`->` S + have/has (not) + V3 + for [time]: ai chưa làm gì trong bao lâu

`->` she là số ít `=>` has

`5)` The last time my father bought me a new book was  `4` months ago.

`->` The last time + S + V-ed + was/were [time] + ago: lần cuối ai làm gì là khi nào

`->` the last time là số ít `=>` was

@nene

`1` I haven't had my haircut since I left her. 

`2` She hasn't kissed me for 5 months.

`3` The last time I saw him was 8 days ago.

`4` She hasn't met her parents for 3 months.

`5` The last time my father bought me a new book was 4 months ago.

`======`

`-` The last time + clause (QKĐ) + was + khoảng thời gian + ago: lần cuối ai làm gì là khi nào

`=` S + has/have + not + PII + for + khoảng thời gian: ai chưa làm gì được bao lâu

`-` The last time + clause (QKĐ) + when + clause (QKĐ): lần cuối ai làm gì là khi ...

`=` S + has/have + not + PII + since + clause (QKĐ): ai chưa làm gì từ khi ...