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: Medicine
[{'content': 'Flourine levels intake required for development of Skeletal Fluorosis \nSelect and explain. \nA. 1.0 - 2.0 ppm, B. 2.0 - 3.0 ppm, C. 3.0 - 6.0 ppm, D. 6-9 ppm', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]