Question

составьте примеры к at/on/in к каждому из них по три примера срочно!

Answer 1

At: 
Meet me in the park at 7pm
I want to study at the university in a couple of years
I was at the dentist's yesterday. 

On: 
Scientists say there's water on Mars
I do aerobics on a regular basis 
My mom always includes bread on the shopping list

In: 
I have been living in Russia since I was born 
I don't like when things are not in their places, especially when I'm looking for something
There are 25 (замените число на ваше) students in my class.