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': 'Mandibular 1st molar has: \nSelect and explain. \nA. 2 roots and 2 canals, B. 2 roots and 3 canals, C. 3 roots and 3 canals, D. 3 roots and 4 canals', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]