TOEFL Listening: ETS-TOEFL听力机经 - _Y2IY451FU4N7WTCP$

According to the professor, which of the following is true of mechanical digestion? A. It does not alter the chemical composition of foods that are ingested. B. It is less important for simple organisms like Protozoa than it is for humans. C. It is a vital step because it helps organisms to create necessary enzymes. D. It leads directly to the absorption of vitamins and minerals used by enzymes.