Please choose the correct answer to the question: When a car engine is started, gasoline is mixed with air and burned. Heat, sound, and chemical products are released. As the engine operates, which of these remains constant?

Answer1: the masses of compounds found in the engine Answer2: the amount of heat in the engine Answer3: the total mass of gasoline Answer4: the total amount of energy

Answer format: answer1/answer2/answer3/answer4