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': 'Right border of the hea in a chest X-ray is not formed by: \nSelect and explain. \nA. WC, B. SVC, C. Right atrium, D. Aoa', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Ans. Aoa', 'role': 'assistant'}]