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': 'Which of the following is a smallest posterior tooth: \nSelect and explain. \nA. Maxillary first premolar, B. Mandibular first premolar, C. Maxillary second premolar, D. Mandibular second premolar', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]