TOEFL Listening: ETS-TOEFL听力机经 - JFE57CB1D31M4Y33P$

Why does the professor mention parts of the corn plant that people eat? A. To make a point about the cost of growing corn as a food crop B. To call attention to a potential conflict between uses of corn C. To describe how ethanol was discovered D. To indicate the part of the corn plant that is not used to make ethanol