This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Medicine
[{'content': 'The earliest chest X-ray change in cystic fibrosis is: \nSelect and explain. \nA. Hyperinflation, B. Ring shadows, C. Marked increase in the bronchovascular markings, D. Prominent right descending pulmonary aery', 'role': 'user'}, {'content': 'Answer: A \nExplanation: The earliest chest x-ray finding in CF lungs is hyperinflation, reflecting small-airways obstruction. Later, signs of luminal mucus impaction, bronchial cuffing, and finally bronchiectasis, e.g., ring shadows, are noticed. Ref: Harrisons Principles of Internal Medicine, 18th Edition, Page 2149.', 'role': 'assistant'}]