This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Radiological anatomy, Subject name: Radiology
[{'content': "What is the structure 'B' marked in lateral chest X-ray below? \nSelect and explain. \nA. Major fissure, B. Minor fissure, C. Azygos fissure, D. Transverse fissure", 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]