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 amount of fluoride in outer enamel is- \nSelect and explain. \nA. 1000-2000 ppm, B. 1500-2500 ppm, C. 2500-3500 ppm, D. 2200-3200 ppm', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Amount of fluoride in the outer enamel is 2,200-3,200 ppm.', 'role': 'assistant'}]