Step 1: Understand the context. Ahmad is going outside in the cold. He needs to wear his coat to stay warm. Step 2: Know the phrasal verb for wearing clothes. "Put on" is the phrasal verb that means to wear or dress in a piece of clothing. Step 3: Check the other options. "Put off" means to delay or remove. "Put up" means to raise or hang. "Put in" means to place inside something. Answer: on