Answer:
C. substances that are used up in a reaction
Explanation:
Substances are combined in a chemical reaction to give rise to other substances. The substances that come together are called REACTANTS while the substances that are produced are called PRODUCTS.
Reactants are used up in the reaction to give rise to new products at the end of the reaction. For example, in the reaction as follows:
6CO2 + 6H2O --> C6H12O6 + 6O2
CO2 (carbon dioxide) and water (H2O) are the REACTANTS of the reaction, which are used up to form glucose and oxygen (products)
