OG 16 verbal

小仙女rachel

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
(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

麻烦问一下各路大神，这个题的D选项为什么不对。
我的理解是：现在的这种方法是唯一方法。这样会变成原文的一个gap/flaw啊，因为原文说，2%的diamonds mined can be successfully treated，那么如果不认为这种方法是唯一方法的话，产量就会多，就攻击了原文的结论啊。

谢谢！！！！
答案对D是这样解释的：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.
我没太搞清楚。。。

小仙女rachel

期待回复

CD!

小仙女rachel 发表于 2017-8-15 13:12
期待回复

我的理解是

(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

選項中有 "currently available" 這個modifier .  

即使世界上有其他還沒"發明"的方法，也不會影響到題目的conclusion( 因為不是currently available的方 法，所以以不會影響到color diamond -> colorless diamond 的比率)

maggiesomi

我对这一题的理解是这样的，flaw in reasoning首先要攻击的不是conclusion的部分而是premise的部分，与weaken题正好相反。所以我们要反过来看，premise里面有哪些不合理的地方去导致了这个conclusion。
例如，我跟我姐姐去麦当劳，我姐姐吃了三个汉堡，我撑的肚子疼。
conclusion是“我撑的肚子疼”，premise是“我俩去吃饭，我姐吃了三个汉堡"。前情跟conclusion完全连不上。前情并没有说我干了什么就忽然撑的肚子疼了。同样的，这道题也是这样。
我们先看conclusion ：the vast majority of colorless diamonds sold by jewelers are naturally colorless. 珠宝商卖的大部分的珠宝都是天然色的，没有人工上色的。
我们再看premise说了什么，premise在说颜色浅的钻石可以跟宝石一样高价。一种廉价宝石可以人工的去色，并且只有通过专业test才能分辨出天然色还是人工去色。但是，这些有颜色的钻石只有2%可以人工上色，其他的有色钻石质量都不行，弄出来不好看不自然。

仔细看看前提跟结论，前提直说了2%的的有颜色的石头可以通过人工上色当成天然色的钻石来卖，却没说，这2%占有所有的钻石的销售额的多少。很可能有一百万个有色钻石，2%的有色钻石去色了，也就是说有两万个有色钻石在当成天然无色钻石在售卖，但是真正的天然钻石可能是有100个。你明白我的意思吗？2%的人工去色钻石不等于 2%的全部正在销售的钻石。所以B才是正确的。
而D选项，怎么去给钻石去颜色，跟本题无关。

maggiesomi

再补充一下，
题目要比较的是，人工去色彩色钻石 跟 天然无色钻石
但是错误的比较了，人工去色彩色钻石 跟 不能去色的彩色钻石