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
Which of the following is not a boundary of the Koch's triangle? 
Select and explain. 
A. tendon of todaro, B. IVC opening, C. coronary sinus ostium, D. septal cusp of tricuspid valve
B: IVC opening
Answer: B: IVC opening 
Explanation: 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