Gastric glands are present in the wall of the stomach which secrete gastric juice containing the digestive enzyme like pepsin, renin, mucus and HCl. The function of these enzymes are as follows:(a) Production of pepsin enzyme that digests proteins.(b) Secretion of mucus for the protection of inner lining of the stomach.(c) Secretion of HCl, which kills the bacteria and foreign harmful organisms in the food. Thus, the correct answer is option D.