2. 外语
  3. Colorless diamonds can command high prices as gemstones. A type of less valuable diamonds can be treated to remove all color. On

Colorless diamonds can command high prices as gemstones. A type of less valuable diamonds can be treated to remove all color. On

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问题 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
选项 A、comparisons between the price diamonds command as gemstones and their value for other uses are omitted
B、information about the rarity of treated diamonds is not combined with information about the rarity of naturally colorless, gemstone diamonds
C、the possibility that colored diamonds might be used as gemstones, even without having been treated, is ignored
D、the currently available method for making colorless diamonds from colored ones is treated as though it were the only possible method for doing so
E、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
答案B
解析 Argument Evaluation
Situation Colored diamonds of a type that comprises 2 percent of all mined diamonds can be treated so that they are not easily distinguishable from more valuable, naturally colorless diamonds, but many are too low in quality for the treatment to be worthwhile.
Reasoning Why do the argument’s premises not justify the conclusion that the vast majority of colorless diamonds sold by jewelers are naturally colorless? Since the type of colored diamonds that can be treated make up only 2 percent of all mined diamonds, and many diamonds of that type are too low in quality for treatment to be worthwhile, the vast majority of mined diamonds must not be treated to have their color removed. However, we are not told what proportion of all mined diamonds are naturally colorless. Naturally colorless diamonds may be far rarer even than the uncommon diamonds that have been treated to have their color removed. Thus, for all we can tell from the passage, it could well be that most colorless diamonds sold by jewelers have been treated to remove all color.
A Even if some types of diamonds command higher prices for uses other than as gemstones, the types discussed in the passage evidently command high enough prices as gemstones to be sold as such by jewelers.
B Correct. The argument does not work if naturally colorless diamonds are rarer than treated diamonds, as they may be for all we can tell from the information provided.
C The argument’s conclusion is only that jewelers sell more naturally colorless diamonds than diamonds treated to be colorless. Whether jewelers sell any colored diamonds or other gemstones is irrelevant.
D The argument only concerns the types of colorless diamonds sold now, not the types that may be sold in the future if other treatment methods are discovered.
E The argument does suggest this difficulty but implies that even so there are too few treated diamonds available for jewelers to sell in place of naturally colorless ones.
The correct answer is B.
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