This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Respiratory Radiology, Subject name: Radiology
[{'content': 'Deep sulcus sign is seen in \nSelect and explain. \nA. Pneumothorax, B. Pleural effusion, C. Tuberculosis, D. Pneumonia', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Deep Sulcus sign is seen On Supine chest x-ray in Expiration phase in a case of Pneumothorax where the lucency of air in the costophrenic angle gives the appearance of a deep sulcus. Other Findings of Pneumothorax on CXR: Absent Bronchoalveolar markings Visceral Pleural Reflection', 'role': 'assistant'}]