`1.` It's 6 years since Mary started learning French.

`2.` It has been 3 years since I last saw her singing

`3.` John hasn't been seen since he was leaving for Edinburgh

`4.` John has been a television presenter for five years.

`5.` My uncle started working as a worker in that factory 10 years ago.

`@` Kiến thức : 

`-` S + last + Ved + time+ ago: Lần cuối cùng làm gì

`=>` S + have/ has +not+ for + time

`=>` It’s + time+ since + S + last + Ved.

`=>` The last time + S + V ed+ was + time + ago.

`-` S + began / started + to V/ V-ing + time ago 

`=>` S + have/has + P2 / been Ving+ for / since ...

`21`. It's `6` years since Mary began to learn French.

`-` Cấu trúc: S+ have/ has+ Vpp+...+ for+ khoảng TG

`≈` It's+ khoảng TG+ since+ S+ began/ started+ to V/ Ving

`22`. It has been `3` years since I last saw her singing again.

`-` Cấu trúc: S+ did+ not+ V+...+ khoảng TG+ ago

`≈` It has been+ khoảng TG+ since+ S+ last+ Ved/ V2

`23`. John hasn't been seen since he was leaving for Edinburgh.

`-` Câu bị động ( thì HTHT, thể phủ định): S+ have/ has+ not+ been+ Vpp+...+ since+ SVO

`24`. John has been a television presenter for five years.

`25`. My uncle started to be a worker in tha factory `10` years ago.

`-` Cấu trúc: S+ began/ started+ to V/ Ving+...+ khoảng TG+ ago

`≈` S+ have/ has+ Vpp+...+ for+ khoảng TG