Bay Area

I think I see the teacher's attempted point, that the carbon and oxygen are combined into carbon dioxide

That teacher's point was nothing but vacuously true bullshit, purely grasping at straws in a desperate attempt to save face. If that were a valid answer, then every element involved participates in both sides of every reaction, so WTF is the point of making a distinction?

Other than blatant bad faith, the only possible way for the teacher to make that argument would be if he's so incompetent he thinks he's teaching "alchemy" instead of chemistry and shit's getting transmuted!