Here's a problem to solve: 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?

Among the 4 following options, which is the correct answer?

- A: Its acidity has been increased.
 
- B: More oxygen has been dissolved in it.
 
- C: Impurities have been removed.
 
- D: Its molecules have higher chemical energies.
 