【GMAT考满分阅读RC题库】Diamonds are almost impossible to detect directly _真题_答案

GWD - 阅读RC - 52

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Diamonds are almost impossible to detect directly because they are so rare: very rich kimberlitepipes, the routes through which diamonds rise, may contain only three carats of diamonds per ton of kimberlite. Kimberlite begins as magma in Earth's mantle (the layer between the crust and the core). As the magma smashes through layers of rock, it rips out debris, creating a mix of liquid and solid material. Some of the solid material it brings up may come from a so-called diamond-stability field, where conditions of pressure and temperature are conducive to the formation of diamonds. If diamonds are to survive, though, they must shoot toward Earth's surface quickly. Otherwise, they revert to graphite or burn. Explorers seeking diamonds look for specks of "indicator minerals" peculiar to the mantle but carried up in greater quantities than diamonds and eroded out of kimberlite pipes into the surrounding land. The standard ones are garnets, chromites, and ilmenites. One can spend years searching for indicators and tracing them back to the pipes that are their source; however, 90 percent of kimberlite pipes found this way are barren of diamonds, and the rest are usually too sparse to mine.

In the 1970's the process of locating profitable pipes was refined by focusing on the subtle differences between the chemical signatures of indicator minerals found in diamond-rich pipes as opposed to those found in barren pipes. For example, G10 garnets, a type of garnet typically found in diamond-rich pipes, are lower in calcium and higher in chrome than garnets from barren pipes. Geochemists John Gurney showed that garnets with this composition were formed only in the diamond-stability field; more commonly found versions came from elsewhere in the mantle. Gurney also found that though ilmenites did not form in the diamond-stability field, there was a link useful for prospectors: when the iron in ilmenite was highly oxidized, its source pipe rarely contained any diamonds. He reasoned that iron took on more or less oxygen in response to conditions in the kimberlitic magma itself-mainly in response to heat and the available oxygen. When iron became highly oxidized, so did diamonds; that is, they vaporized into carbon dioxide.

The passage suggests that the presence of G10 garnet in a kimberlite pipe indicates that

Athe pipe in which the garnet is found has a 90% chance of containing diamonds
Bthe levels of calcium and chrome in the pipe are conducive to diamond formation
Cthe pipe passed through a diamond-stability field and thus may contain diamonds
Dany diamonds the pipe contains would not have come from the diamond-stability field
Ethe pipe's temperature was so high that it oxidized any diamonds the pipe might have contained

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正确答案: C

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小倩猪

应该选C，B“the levels of calcium and chrome in the pipe are conducive to diamond formation”，说的是Pipe中的calcium and chrome含量对钻石的形成有利，但是原文说的是G10的calcium and chrome含量，张冠李戴，应该是错的。
“Geochemists John Gurney showed that garnets with this composition were formed only in the diamond-stability field,”，第一段说diamond-stability field有利于钻石的形成，所以连起来就是G10在diamond-stability field中，所以可能形成钻石啦，选C

2016-11-26 20:38:50 IP属地：上海举报

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与锅回复小倩猪

B的分析错了，你这个是歪打正着，句子都没分析清楚
...the chemical signatures of indicator minerals found in diamond-rich pipes as opposed to those found in barren pipes. For example, G10 garnets, a type of garnet typically found in diamond-rich pipes，这个focus on chemical signature，然而G10就是一种indicator minerals（三者之一，在最后一段说明了），并没有张冠李戴

2021-09-11 19:54:07 IP属地：局域网举报

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与锅回复与锅

说错了，在第一段末尾说了是：G，I，和C

2021-09-11 19:54:58 IP属地：局域网举报

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KunKun你最棒回复小倩猪

谢谢你！

2018-07-16 22:53:30 IP属地：河南举报

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gbyhats

我的理解：

这题的答案是C，低钙高铬的G10石榴石只在易形成钻石的地方出现

--

原文：
Geochemists John Gurney showed that **garnets with this composition** were formed only in the **diamond-stability field**.

同时关于B：

【低钙高铬的G10石榴石】和【钻石】【同时出现】不代表低钙高铬的环境【能产生】钻石，也可以是【低钙高铬的G10石榴石】在【不易产生钻石的环境】很容易就被破坏，还没到达地表就消失了

【同时发生】但不一定是【因果关系】是一种CR题型，一个例子可以见一道GWD CR题：It is true of both men and women that those who marry as young adults live longer...

2015-03-29 18:09:26 IP属地：局域网举报

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garyzhai

个人觉得应该选C
因为B选项中出现了，Conducive是原文中出现过的词，根据我做阅读的经验，若选项中出现与原文一模一样的词，该选项在文中的位置应尽量靠近问题所问的对象，而conducive与G10并不在同一段。相比之下C选项是比B近很多。这是个人经验之谈
再说，问并无提示G10的成分与钻石相似，G10的成分只能作为判断PIPE的指标。该题是Indicate而不是infer。所以不应该做猜测。
前面有评论PASS THROUGH指一部分在，也有可能另一部分不在，与ONLY不符。我觉得这是推理方向错了。题目是indicate，应该由文中内容推选项，而不是用选项去倒推或质疑。所以说，既然是only，它就应该PASS THROUGH
还有，我从其他地方的参考资料也显示该题答案是C

2014-11-21 11:02:26 IP属地：局域网举报

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feenes

定位：Geochemists John Gurney showed that garnets with this composition were formed only in the diamond-stability field; more commonly found versions came from elsewhere in the mantle. 这里说只有在diamond-stability field里面才能找到这种G10，联系上下文可以知道化学元素组成是影响钻石形成的。而A的90%在文中从来没有出现过，无中生有了，又或者说是绝对化了。

2016-05-11 11:27:23 IP属地：局域网举报

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shirleyyy1228

B选项错在
第一段说了Some of the solid material it brings up may come from a so-called diamond-stability field, where conditions of pressure and temperature are conducive to the formation of diamonds.所以是这个diamond-stability field有利于diamonds的形成，而不是the levels of calcium and chrome。

2018-10-12 05:12:26 IP属地：北京举报

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angelyaer

In the 1970\'s the process of locating profitable pipes was refined by focusing on the subtle differences between the chemical signatures of indicator minerals found in diamond-rich pipes as opposed to those found in barren pipes. For example, G10 garnets, a type of garnet typically found in diamond-rich pipes, are lower in calcium and higher in chrome than garnets from barren pipes.

2016-08-23 12:15:17 IP属地：上海举报

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LysaEsperando

All in one课程上，老师给的答案是C。

2016-09-02 15:47:22 IP属地：浙江举报

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armaniyen

重點在於
the levels of calcium and chrome \"in the pipe\" 不等於
G10 的 Cal and Chrome Level --> 很明顯可排除 B 認為此答案應該要更正

至於質疑 C
--> the pipe passed through a diamond-stability field
文中很清楚表明
1. kimberlitepipes, the routes through which diamonds rise,
2. G10 garnets, a type of garnet typically found in diamond-rich pipes
3. G10 garnets were formed only in the diamond-stability field;

2016-09-03 20:50:27 IP属地：中国台湾举报

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小FF

个人认为B中因果倒置，原文G10 garnets, a type of garnet typically found in diamond-rich pipes, are lower in calcium and higher in chrome than garnets from barren pipes. 是指再钻石丰富的pipe（因）中产生了G10这种物质（果），G10具有 lower in calcium and higher in chrome特点；但是，B的意思是这个特点（因）导致了diamond formation（果）。
C原文“G10 garnets, a type of garnet typically found in diamond-rich pipes, ... that garnets with this composition were formed

2018-07-21 23:11:52 IP属地：上海举报

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小FF 回复小FF

补充完：in the diamond-stability field ”说明pipes富含G10 而G10只能在diamond-stability的地方形成，从而合理推出pipe经过了diamond-stability的地方。总的来说，我觉得这道题这么考挺容易让人混淆的。

2018-07-21 23:12:11 IP属地：上海举报

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bamboogo

OA should be C

2016-10-23 21:30:46 IP属地：北京举报

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