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
'Velcro' crackles are heard in: 
Select and explain. 
A. Lung cancer, B. Pneumothorax, C. Pulmonary fibrosis, D. Pleural effusion
C: Pulmonary fibrosis
Answer: C: Pulmonary fibrosis 
Explanation: Diseases that result in fibrosis of the interstitium (e.g., IPF) also result in crackles that sound like Velcro being ripped apart.