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': 'Lethal dose of fluoride is: \nSelect and explain. \nA. 250 milligrams, B. 500 milligrams, C. 5 grams, D. 10 grams', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]