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': 'Root crown ratio of permanent teeth is about \nSelect and explain. \nA. 2:01, B. 1:02, C. 4:01, D. 1:04', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]