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
[{'content': 'Coronary sinus opens into: \nSelect and explain. \nA. IVC, B. Right atrium, C. Left atrium, D. Great cardiac vein', 'role': 'user'}, {'content': 'Answer: B \nExplanation: B - B.D. Chaurasia, Vol.l 4,h ed, p. 251', 'role': 'assistant'}]