Here are the completed sentences using "used to" or "didn't use to":

1. In my childhood, there **didn't use to be** so many high buildings here. There were parks.
2. People **used to write** with pen, but now they use computers.
3. My brother **used to play** football, but an injury stopped him from playing.
4. In my grandfather's youth, people **used to travel** by car. They rode horses.
5. I **used to walk** to school, but two weeks ago I got a bike so I ride it every day.
6. My sister **didn't use to swim** when we go to the beach because she was afraid of water.
7. Mr. Lam **used to watch** television in the morning. He did it in the evening.
8. David was a good climber in his youth. He **used to climb** very high mountains.
9. My parents **didn't use to buy** me expensive toys as we were not rich.
10. We **used to shop** in the town market. We bought fish, fruit, and vegetables.