TOEFL Listening: ETS-TOEFL听力机经 - O39BJ532PK4D5LT8P$

Why does the professor discuss the human digestive system? A. To describe how the function of enzymes was discovered. B. To give an example of what enzymes are and how they work. C. To explain how the textile industry began to use enzymes. D. To show that some enzymes are more powerful than others.