This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Respiratory, Subject name: Medicine
[{'content': 'Pulmonary crackles are frequently heard in? \nSelect and explain. \nA. Pneumothorax, B. Pulmonary fibrosis, C. Pleural effusion, D. Lung cancer (secondary)', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Ans. B. Pulmonary fibrosisCrackles are produced by fluid in alveoli or by fibrotic airways. Therefore, they can be heard in patients with pulmonary fibrosis or congestive heart failure.', 'role': 'assistant'}]