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: Radiology
[{'content': 'Lt border of the hea in C.X.R. is formed by: \nSelect and explain. \nA. Pul.aery, B. Pul. vein, C. Abdominal aoa, D. All', 'role': 'user'}, {'content': 'Answer: A \nExplanation: A i.e. Pulmonary aery', 'role': 'assistant'}]