Please choose the correct answer to the question: A gasoline is advertised as "releasing fewer pollutants" when it is used in cars. For this claim to be accurate, what has most likely happened to the gasoline?

Answer1: Its acidity has been increased. Answer2: More oxygen has been dissolved in it. Answer3: Impurities have been removed. Answer4: Its molecules have higher chemical energies.

Answer format: answer1/answer2/answer3/answer4