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': "'Velcro' crackles are heard in: \nSelect and explain. \nA. Lung cancer, B. Pneumothorax, C. Pulmonary fibrosis, D. Pleural effusion", 'role': 'user'}, {'content': 'Answer: C \nExplanation: Diseases that result in fibrosis of the interstitium (e.g., IPF) also result in crackles that sound like Velcro being ripped apart.', 'role': 'assistant'}]