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': 'Structure forming right border of heart – a) SVCb) IVCc) Rt. atriumd) Lt. atrium appendagee) Pulmonary vessels \nSelect and explain. \nA. ab, B. abc, C. acd, D. bcd', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Right margin of heart is formed by SVC, right atrium, and IVC from above downward.', 'role': 'assistant'}]