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': 'Plasma  fluoride  level expected in a  healthy, fasting, long-term resident of a community with a water fluoride level of 1 ppm is approximately? \nSelect and explain. \nA. 0.01 ppm, B. 0.012 ppm, C. 0.015 ppm, D. 0.019 ppm', 'role': 'user'}, {'content': 'Answer: D \nExplanation: The\xa0 ionic\xa0 fluoride\xa0 is of\xa0 public health significance. It varies\xa0 according\xa0 to the concentration of fluoride in the drinking water.\xa0 Its\xa0 plasma\xa0 concentration\xa0 is approximately\xa0 twice\xa0 as\xa0 high\xa0 as\xa0 that associated with the blood cells. Since plasma fluoride\xa0 levels\xa0 are\xa0 not\xa0 homeostatically regulated, there is no normal physiologic concentration.\xa0 Plasma\xa0 fluoride\xa0 level expected in a\xa0 healthy, fasting, long-term resident of a community with a water fluoride level of 1 ppm is approximately 1 µM (0.019 ppm). There is evidence that plasma fluoride levels increase slightly with age.', 'role': 'assistant'}]