Design a short experimental test to confirm that gastric pH is necessary for pepsin activation, including a control condition, and predict the expected outcome.

• A. Heat pepsinogen samples to 95°C to denature them and then add substrate to show pepsinogen is activated by heat rather than acid, predicting cleavage under heated conditions only.
• B. Incubate pepsinogen in water and in saline and measure pH change; expect pepsinogen to lower pH autonomously and therefore be active regardless of initial gastric pH.
• C. Incubate pepsinogen with a protein substrate at low pH (e.g., pH 2) and at neutral pH (pH 7) as control; measure peptide formation → expect peptide cleavage only at low pH confirming pepsinogen activation requires acidic pH.
• D. Compare protein digestion in the mouth and stomach of volunteers after they take antacid or placebo and attribute any changes in digestion solely to salivary proteases without measuring gastric pH directly.

Answer: (C)