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 shortest root on a maxillary first molar is: \nSelect and explain. \nA. Mesio-buccal, B. Disto-buccal, C. Lingual, D. All are of equal length', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]