Stomach's Digestive Role

Steps:

• Recall the stomach's primary functions: mechanical churning, secretion of gastric juices, and initial protein breakdown.
• Identify secretions: hydrochloric acid for pH and pepsinogen activation into protease pepsin.
• Evaluate options against these functions to eliminate mismatches.
• Confirm the best match based on accurate biological processes.

Why D is correct:

• The stomach lining secretes pepsin (a protease enzyme) and hydrochloric acid (a strong acid) to break down proteins into peptides, as defined in human digestive physiology.

Why the others are wrong:

• A: Indigestible material absorption occurs in the large intestine, not the stomach.
• B: Bile emulsifies fats in the small intestine; proteases work in the stomach, but not together with bile there.
• C: Starch digestion begins in the mouth via salivary amylase, not the stomach.

Final answer: D