TOEFL Listening: TPO-TOEFL阅读TPO - C5S399OR6CMIQ354N$

In paragraph 2, the author compares the teeth of cows, horses, rabbits, and mice to grindstones in order to explain A. how certain kinds of teeth aid digestion B. how the teeth of some familiar mammals differ from those of dinosaurs C. why the back teeth of herbivores are larger than those of carnivores D. why the back teeth of carnivores are just as sharp as their front teeth