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.
The passage suggests which of the following about the effect of fluoride on humans?
- A The effect of fluoride intake from water and air is relatively difficult to monitor.
- B An intake of 4 milligrams over a long period of time usually leads to a skeletal disorder in humans.
- C An intake of slightly more than 4 milligrams for only a few months is not likely to be life-threatening.