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': 'The average diameter of coronal dentinal tubules near the pulp is: \nSelect and explain. \nA. 0.2-0.5 microns, B. 2-3 microns, C. 0.2-0.3 microns, D. 7 microns', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]