Using a gasoline engine requires burning gasoline, and for every one gallon of gasoline an engine burns, one gallon of water is produced as a by-product. Given these facts, what is NOT a byproduct of using a gasoline engine among the following options:
- chickenpox
 - carbon dioxide
 - carcinogens
 - Collagen
 - water
 - warmth
 - loose dirt
 - uranium


 

        uranium 