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: Pathology
[{'content': 'Pioneer bacteria in dental caries are in \nSelect and explain. \nA. Enamel, B. Dentin, C. Pulp, D. Cernenturn', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]