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
Flourine levels intake required for development of Skeletal Fluorosis 
Select and explain. 
A. 1.0 - 2.0 ppm, B. 2.0 - 3.0 ppm, C. 3.0 - 6.0 ppm, D. 6-9 ppm
C: 3.0 - 6.0 ppm
Answer: C: 3.0 - 6.0 ppm 
Explanation: None