The author mentions the cow and the horse in paragraph 2 in order to A. distinguish the functioning of their digestive systems from those of East African mammals B. emphasize that their relatively large body size leads them to have feeding practices similar to those of East African mammals C. illustrate differences between ruminants and nonruminants through the use of animals likely to be familiar to most readers D. emphasize similarities between the diets of cows and horses and the diets of East African mammals