Answer: B. product
The molecules upon which enzymes act are known as substrates. These substrates are later converted into different molecules known as products. Generally, enzymes, which are biological catalysts of the reactions of the body, are proteins with the ability to bind substrates in their active state and then chemically modify the bound substrate gotten to form the product of the reaction. The substrate is also known as the reactant. So, the enzyme binds with the substrate, a series of reactions happen and the product is released from the active site of the enzyme. Since enzymes are catalysts, they help in altering the rate of the reaction by lowering the activation energy of the reaction but are in no way part of the reaction itself.