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': "Dean's fluorosis index was modified in the year \nSelect and explain. \nA. 1934, B. 1938, C. 1942, D. 1945", 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]