Man cannot digest cellulose. Herbivores, viz.. rabbits, cows, can. The most important reasons for this are that:

A. They have very efficient grinding teeth
B. They possess an enlarged section of the gut containing bacterial which break the cellulose for them
C. They produce the enzyme cellulase which digests the cellulose; human beings do not make this enzyme
D. Human beings do not need to digest cellulose