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
Right heart border is mainly formed by 
Select and explain. 
A. Right atrium, B. Superior vena cava, C. Right ventricle, D. Inferior vena cava
A: Right atrium
Answer: A: Right atrium 
Explanation: Right heart border: SVC, Rightatrium, Ivc mainly by Right atrium.