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
[{'content': 'Recommended convergence between opposing axial walls, which optimize retention, is \nSelect and explain. \nA. 6 degree, B. 30 degree, C. 15 degree, D. 45 degree', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]