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
The amount of fluoride in outer enamel is- 
Select and explain. 
A. 1000-2000 ppm, B. 1500-2500 ppm, C. 2500-3500 ppm, D. 2200-3200 ppm
D: 2200-3200 ppm
Answer: D: 2200-3200 ppm 
Explanation: Amount of fluoride in the outer enamel is 2,200-3,200 ppm.