Son asked: Why cars need gasoline?

My boys, like most of the boys out there, are obsessed with machines, especially cars. They like to watch Cars movies and own tons of toy cars. They also like to observe cars in real life and ask a lot of questions about them.

My elder boy, Pham Duy Khoi (PDK), and I had the below conversation not too long ago.

PDK: Daddy, why cars need gasoline?
Me (PDD): Can you keep on playing when you're hungry?
PDK: No, I can't. I need to have some food.
PDD: See, cars can go for a while then it gets hungry. It'll need to eat again, just like you, and gasoline is food for cars.
PDK: But, Daddy, cars can't eat right?
PDD: Correct, you don't see cars eat. But whenever a car visits a gas station, they usually get more gasoline to go further.

PDK nodded, and again I survive another intellectual challenge from a toddler.