1. Toan used to play badminton when he was small.

2. She used to go to scholl on foot when she was 15 years old.

3. My hair used to long and black 5 years ago. Now it's short and yellow.

4. His father used to be a teacher. Now he is retired.

5. Folk songs used to be so popular in the past. Now they aren't anymore.

6. There used to be less traffic congestion 10 years ago. Now it becomes more common.

7. My grandmother used to be the prettiest girl in the village.

8. My room used to be blue last year. Now I have painted it pink. 

9. This singer used to have little money when she was small.

10. People used to write letters to each other. Now they have mobile phones.

Về cách sử dụng công thức "used to", bạn chỉ cần áp dụng công thức là ra thôi
Công thức "used to": S + Ved + O → S + used to V bare + O

( Ved là động từ ở thì quá khứ; S là chủ ngữ; V bare là động từ nguyên ( ở thì hiện tại đơn) còn O là tân ngữ) 

Đáp án:

1. Toan used to play badminton when he was small.

2. She used to go to school on foot when she was 15 years old.

3. My hair used to be long and black 5 years ago.

4. His father used to be a teacher in our school.

5. Folk songs used to be so popular in the past.

6. There used to be less traffic congestion 10 years ago.

7. My grandmother used to be the prettiest girl in the village.

8. My room used to be blue last year. 

9. This singer used to have little money when she was small.

10. People used to write letters to each other. 

Áp dụng công thức:
S + Ved ..

→ S + used to + Vo..