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': 'What is the optimum depth for a pinhole in a tooth with a vital pulp \nSelect and explain. \nA. 4-5 mm, B. 2-3 mm, C. 2 mm, D. 1-1.5 mm', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]