Bonjour! Je vais essayer! :D
Ex1
1. That's the best thing you can do.
2. My brother is the oldest in his class.
3. This is the cheapest radio in the shop.
4. It was the most dangerous experience of my life.
Ex2
1. It's the most dangerous city in the world.
2. I think I am the tallest (tall - haut).
3. Who is the most stupid/stupidest (les deux sont corrects) boy of the school.
4. It's the easiest exercise of the test ("control")
Ex3
1. What is the largest city in your country?
2. Who is the most famous singer in your country?
3. Who is the most intelligent person you know?
4. What was the happiest day in your life?
Voila! J'espere avoir t'aide! :)