Detailed Instructions: Given a scientific passage and an answer, generate a question for the given answer.
Q: Passage: A refrigerator is an example of a cooling system. Another example is an air conditioner. The purpose of any cooling system is to transfer thermal energy in order to keep things cool. A refrigerator, for example, transfers thermal energy from the cool air inside the refrigerator to the warm air in the kitchen. If you've ever noticed how warm the back of a running refrigerator gets, then you know that it releases a lot of thermal energy into the room. Answer: thermal
A:
The purpose of any cooling system is to transfer what type of energy in order to keep things cool?