This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Thorax, Subject name: Anatomy
The arrow marked structure drains into: 
Select and explain. 
A. Right atrium, B. Left atrium, C. Right ventricle, D. Left ventricle
A: Right atrium
Answer: A: Right atrium 
Explanation: Ans. A. Right atriumThe arrow marked structure is coronary sinus and it drains into right atrium.