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
Pulmonary crackles are frequently heard in? 
Select and explain. 
A. Pneumothorax, B. Pulmonary fibrosis, C. Pleural effusion, D. Lung cancer (secondary)
B: Pulmonary fibrosis
Answer: B: Pulmonary fibrosis 
Explanation: 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.