Using a gasoline engine requires burning gasoline.
For every one gallon of gasoline an engine burns, one gallon of water is produced as a by-product.
Using a gasoline engine produces water as a by-product.
What is NOT a byproduct of using a gasoline engine?
Options:
1. chickenpox
2. carbon dioxide
3. carcinogens
4. Collagen
5. water
6. warmth
7. loose dirt
8. uranium