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': 'DMF index was given by: \nSelect and explain. \nA. Mien, Palmar, Knutson and Henry in 1938, B. Moller in 1966, C. Gruebbel in 1994, D. Katz in 1980', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]