Question

Which of the following supplies the heat for the hot reservoir in a car's engine?

mixing gasoline with air

cooling the exhaust gases

igniting the gas-air mixture

venting the exhaust gases

Answer 1

@aaronq

Answer 2

@hartnn @robtobey

Answer 3

Venting the exhaust gasses

Answer 4

Please, do not provide ready-made answers without
1. explaining
2. being certain your answer is the right one

Answer 5

(*previously posted comment* Oops, it seems that was a direct answer. I have deleted it accordingly)

Okay. Let me ask you a question: What do you think causes heat, and what do you think does not?