The correct option is A If both assertion and reason are true and reason is the correct explanation of assertion.
The cattle, buffaloes, goats, sheep, deer and camels are herbivorous animals that feed on plant leaves, twigs, etc. Their stomach consists of 4 chambers: rumen (paunch), reticulum (honeycomb), omasum (Psalterium) and abomasum (rennet). In the rumen, food undergoes mechanical and chemical breakdown. Mechanical breakdown results from thorough churning brought about by muscular contractions and aided by a cornified surface of villi. The chemical breakdown is caused by symbiotic micro-organisms bacteria such as Ruminococcus and ciliate such as Entodinium caudatum. These microorganisms live as symbionts in the rumen and reticulum of the stomach of the ruminants (e.g., cows and buffaloes) and in the large intestine of other herbivorous mammals (e.g., horses and donkeys) and release enzyme, cellulases, which acts on cellulose and simplify it to short-chain fatty acids. Cellulose is not digested by the human beings.