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: Anatomy
[{'content': 'Anterior cardiac veins open into: \nSelect and explain. \nA. Right atrium, B. Great cardiac vein, C. Coronary sinus, D. Marginal vein', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Right atrium', 'role': 'assistant'}]