The correct option is C Zymogens
In a zymogen, a peptide blocks the active site of the enzyme. Cleaving off this peptide activates the enzyme. The peptidase in the stomach is pepsin. Pepsin works optimally in the acidic environment of the stomach, being active at pH 2 - 3, but becoming inactivated, when the pH is above 5. The chief cells at the base of the gastric glands secrete the zymogen, which is called pepsinogen. Activation of pepsinogen starts, when hydrocholoric acid (HCl), which is secreted by the parietal cells partially activates pepsinogen. This partially active enzyme, then cleaves the peptide from other pepsinogen molecules to form active pepsin.