`1` I used to smoke `10` years ago 

`=>` S + used to + V : Đã từng làm việc gì nhưng giờ ko còn xảy ra nữa 

`2`  John often went on food when he was a little boy 

`=>` S + used to + V 

`=` S + often + Ved / V2 + O 

`3` He used to to play tennis better than  now  

`-` Tạm dịch : Anh ấy từng chơi tennis giỏi hơn bây giờ 

`4` It took me `20` minutes to walk to school 

`=>` It took + O + time + to + V : Mất bao nhiêu thời gian làm việc gì đó

`5` While I was having dinner , the phone rang

`=>` While + quá khứ tiếp diễn , quá khứ đơn : khi hành động " tôi đang ăn tối" diễn ra trong quá khứ thì hành động " điện thoại reo lên " xen vào 

1. I used to smoke.

S + gave up + V_ing

->S + used to + V.

2. John often went on bare foot when he was a little boy.

S + used to + V

->S + usually/always + V_qk 

3. He used to play soccer better than he does now.

S + do/does + not + V + as + adv + as + S + used to + V.

->S + used to + V + adv+er/more + adv + than + S + do/does now.

4.  It took me 20 minutes to walk to school.

S + V + in + khoảng thời gian

->It took + S + khoảng thời gian + to + V.

5. While I was having dinner, the phone was ringing.

Trong khoảng thời gian, S + V.

->While S + be + V_ing, S + be + V_ing