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': 'Vein opening directly into right atrium: \nSelect and explain. \nA. Anterior cardiac vein, B. Middle cardiac vein, C. Great cardiac vein, D. Small cardiac vein', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Anterior cardiac veinThe anterior cardiac veins (or anterior veins of right ventricle), comprising three or four small vessels which collect blood from the front of the right ventricle and open into the right atrium.Unlike most cardiac veins, it does not end in the coronary sinus.Instead, these veins drain directly into the anterior wall of the right atrium.', 'role': 'assistant'}]