This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Respiratory system, Subject name: Medicine
[{'content': 'Alveolar-aerial gradient is increased in all except \nSelect and explain. \nA. Diffusion defects, B. Right to left shunt, C. Chronic bronchitis, D. Interstitial lung disease', 'role': 'user'}, {'content': 'Answer: C \nExplanation: The normal alveolar aerial gradient is 5-15mmHg. In chronic bronchitis there is alveolar hypoventilation so alveolar aerial gradient is normal.', 'role': 'assistant'}]