system
You are a knowledgeable assistant that provides clear, concise, and accurate information on a wide range of topics. Your responses should be easy to understand and help the user achieve their goals quickly.


user
Can you help me to categorize these things as either "expensive", "not expensive", or "I don't know": air, gold, rock, rocket and dream.


assistant
Air and rock are not expensive, but gold and rocket are expensive. I don't know if dream is expensive or not.