GRE Reading Comprehension
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Source: XDF
The success of fluoride in combating dental decay is well established and, without a doubt, socially beneficial. However, fluoride's toxic properties have been known for a century. In humans excessive intake (for adults, over 4 milligrams per day) over many years can lead to skeletal fluorosis, a well-defined skeletal disorder, and in some plant species, fluoride is more toxic than ozone, sulfur dioxide, or pesticides.
Some important questions remain. For example, the precise lower limit at which the fluoride content of bone becomes toxic is still undetermined. And while fluoride intake from water and air can be evaluated relatively easily, it is much harder to estimate how much a given population ingests from foodstuffs because of the wide variations in individual eating habits and in fluoride concentrations in foodstuffs.
One function of the second paragraph of the passage is to
- A raise doubts about fluoride's toxicity
- B introduce the issue of fluoride's toxicity
- C differentiate a toxic from a nontoxic amount of fluoride
- D indicate that necessary knowledge of fluoride remains incomplete
- E discuss the foodstuffs that are most likely to contain significant concentrations of fluoride