People have studied chemistry d. since fire was discovered.

While early people may not have known chemistry, they have unknowingly performed it while doing day-to-day survival tasks. Fire, in particular, is a chemical reaction at work. Fire is a manifestation of some burning material's oxidation as it undergoes a combustion reaction. People who made fire early on made fire knowingly, which means that they performed a chemical reaction anticipating some previously established result even if they did not know it at the time.