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': 'Shifting dullness is the characteristic sign of: \nSelect and explain. \nA. Hydropneumothorax, B. Pneumothorax, C. Consolidation, D. Collapse', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]