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': 'Triangle of koch is made by: \nSelect and explain. \nA. Posterior leaf-let of mitral valve, B. Coronary sinus opening, C. Superior vena cava opening, D. All', 'role': 'user'}, {'content': 'Answer: B \nExplanation: B i.e. Coronary sinus opening', 'role': 'assistant'}]