This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Surfaces and Grooves, Subject name: Anatomy
[{'content': "Which of the following is not a boundary of the Koch's triangle? \nSelect and explain. \nA. tendon of todaro, B. IVC opening, C. coronary sinus ostium, D. septal cusp of tricuspid valve", 'role': 'user'}, {'content': "Answer: B \nExplanation: Koch's triangle boundaries tendon of Todaro opening of coronary sinus at the base septal cusp of tricuspid valve (. atrio ventricular valve) AV node at apex", 'role': 'assistant'}]