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': 'On which of the following permanent teeth is it most difficult to distinguish between mesial and distal aspects? \nSelect and explain. \nA. Maxillary central incisor, B. Mandibular central incisor, C. Mandibular lateral incisor, D. Mandibular second premolar', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]