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 has the largest relative mesiodistal dimension of the root canal? \nSelect and explain. \nA. Maxillary Lateral incisor, B. Mandibular second premolar, C. Palatal root of maxillary 1st molar, D. Distal root of the mandibular 1st molar', 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]