The classic pathway of complement activation begins when the protein C1 binds to:

Correct Answer: C

Rationale: C1 binds antigen-antibody complexes, initiating classic complement.

Correct Answer: D

Rationale: Increased respiration removes CO2, raising pH in acidosis.

Correct Answer: A

Rationale: Duodenal ulcers typically occur within 3 cm of the pylorus, commonly on both anterior and posterior walls, due to acid exposure and Helicobacter pylori infection.

Correct Answer: A

Rationale: Crohn's disease is characterized by transmural inflammation often leading to fistulas, with skip lesions rather than continuous involvement.

Correct Answer: D

Rationale: The d-xylose test assesses small bowel absorption, not pancreatic function, unlike the other tests which evaluate pancreatic enzyme output or damage.