The answer would be c. the new substances that are formed during the reaction. The products are what you end up with after the reaction. For instance, the products of photosynthesis are glucose and oxygen because that's what plants make as a result. The reactants are what are used to start the reaction. The reactants in photosynthesis are carbon dioxide, water and sunlight since that's what plants need in order to start the process. Hope this helped! :)