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题库 / OG2017V-CR-167
Colorless diamonds can command high prices as gemstones. A type of less valuable diamonds can be treated to remove all color. Only sophisticated tests can distinguish such treated diamonds from naturally colorless ones. However,only 2 percent of diamonds mined are of the colored type that can be successfully treated, and many of those are of insufficient quality to make the treatment worthwhile. Surely, therefore, the vast majority of colorless diamonds sold by jewelers are naturally colorless.
A serious flaw in the reasoning of the argument is that
comparisons between the price diamonds command as gemstones and their value for other uses are omitted
information about the rarity of treated diamonds is not combined with information about the rarity of naturally colorless, gemstone diamonds
the possibility that colored diamonds might be used as gemstones, even without having been treated, is ignored
the currently available method for making colorless diamonds from colored ones is treated as though it were the only possible method for doing so
the difficulty that a customer of a jeweler would have in distinguishing a naturally colorless diamond from a treated one is not taken into account
找gap题。
没有同时考虑treated diamonds和colorless, gemstone diamonds的稀缺，文章只考虑了treated diamonds的稀缺，如果colorless, gemstone diamonds同样稀缺，那么，柜台售卖的不一定大部分都是colorless, gemstone diamonds
C项，直接在反前提
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