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 element fluoride was described by Churchill in: \nSelect and explain. \nA. 1934, B. 1942, C. 1931, D. 1941', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]