The correct option is D proteins
The gastric gland releases hydrochloric acid, pepsin and mucus. Pepsin is responsible for the breakdown of proteins into peptides. Pepsin requires an acidic medium to exert its action and so the acid secreted serves this function. Hydrochloric acid also kills the unwanted microbes present in the stomach. The mucous protects the stomach lining from the corrosive action of the acid.