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: Surgery
[{'content': 'Most serious injury is at \nSelect and explain. \nA. open pneumothorax, B. diaphragmatic injury, C. Flail chest, D. Single rib fracture', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Answer- A. open pneumothoraxThis is a large open defect in the chest (> 3 cm), leading to equilibration between intrathoracic and atmospheric pressure.Air accumulates in the hemithorax (rather than in the lung) with each inspiration, leading to profound hypoventilation on the affected side and hypoxia.', 'role': 'assistant'}]