TOEFL Listening: ETS-TOEFL听力机经 - 8T44PCQ4EX385E2ZP$

According to the professor, what are the main functions of beneficial bacteria that normally live in the digestive system? A. They help the body process complex carbohydrates. B. They consume the bacteria that cause digestive problems. C. They produce some vitamins that the body cannot make on its own. D. They slowdown the absorption of proteins. E. They prevent bad bacteria from obtaining enough nutrients.