`1,` My mother used to work at a restaurant 3 years ago.

`2,` He used to be the president of Student Union.

`3,` There used to be many tree-lined streets in my hometown.

- Cấu trúc used to (từng làm gì, giờ không còn làm nữa):

`(+)` S + used to + Vinf + O

`(-)` S + didn't + use to + Vinf + O

`(?)` Did + S + use to + Vinf  + O

1.My mother used to work at a restaurant 3 years ago

2.He used to be the President of Student Union

3.There used to be many tree-lined streets y hometown

_Cấu trúc : S used to be/V ( nguyên thể ) : đã từng làm gì

_Bổ trợ : S tobe used to V-ing : quen với việc làm gì