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
Structure forming right border of heart – a) SVCb) IVCc) Rt. atriumd) Lt. atrium appendagee) Pulmonary vessels 
Select and explain. 
A. ab, B. abc, C. acd, D. bcd
B: abc
Answer: B: abc 
Explanation: Right margin of heart is formed by SVC, right atrium, and IVC from above downward.