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: Dental
Recommended convergence between opposing axial walls, which optimize retention, is 
Select and explain. 
A. 6 degree, B. 30 degree, C. 15 degree, D. 45 degree
A: 6 degree
Answer: A: 6 degree 
Explanation: None