Final answer:
In the digestive system, the breakdown of carbohydrates by enzymes in the saliva represents a chemical change, where substances like amylase catalyze the transformation of starch into sugars.
Step-by-step explanation:
In the digestive system, the process that is best classified as a chemical change is c) Enzymes in the saliva break down carbohydrates. Digestion in the mouth involves both mechanical and chemical processes, where the chemical aspect includes the breaking down of carbohydrates by enzymes such as amylase. This enzyme catalyzes the hydrolysis of starch into sugars, which is a classical chemical change because it results in the formation of new substances.