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': 'The structure marked with arrow is: \nSelect and explain. \nA. Coronary artery, B. Pulmonary artery, C. Arch of aorta, D. Pulmonary vein', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]