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GMAT 考满分题库

GWD - 阅读RC - 53
题目材料
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.

According to the passage, Gurney refined the use of ilmenites in prospecting for diamonds in which of the following ways?

  • AHe found that ilmenites are brought up from the mantle by kimberlite pipes and erode out into the surrounding land in greater quantities than diamonds.
  • BHe found that since ilmenites do not form in the diamond-stability field, their presence indicates the absence of diamonds.
  • CHe showed that highly oxidized iron content in ilmenites indicates a low survival rate for diamonds.
  • DHe found that when the iron in ilmenites is highly oxidized, conditions in the magma were probably conducive to the formation of diamonds.
  • EHe showed that ilmenites take on more or less oxygen in the kimberlite pipe depending on the concentration of diamonds.
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正确答案: C

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佳l林jalo

佳l林jalo

lovely老师已经被我抓到了,老规矩,赞一下喂一口屎

2017-11-24 17:41:22  IP属地:广东
kaka0806

kaka0806

【there was a link useful for prospectors: when the iron in ilmenite was highly oxidized, its source pipe rarely contained any diamonds. 】
prospector的重点在于ilmenite+oxidized =rarely diamonds
B只强调了ilmenite没有oxidized,并且rarely换成了absence绝对化了,所以错误

2015-09-17 15:27:26  IP属地:北京
ginozobe

ginozobe

B應該不是absence的錯吧,不能用對字眼的吧,應該是因果出現問題

2014-12-18 17:40:34  IP属地:局域网
lynnbrair

lynnbrair

像这种问专家观点的问题,第一件事就是找到在这专家名字哪儿出现,然后前后文都要看一下,重点是后面的几句。注意语气变换和上下文连接、

2012-08-10 15:12:00  IP属地:保留地址
突然很适合你

突然很适合你

看到B直接就选了。。。

2018-01-06 19:29:41  IP属地:广东
hjikod

hjikod

B选项不是因为ilmenites的出现表明了the absence of diamonds, 而是因为when the iron in ilmenite was highly oxidized, its source pipe rarely contained any diamonds 和 when iron became highly oxidized, so did diamonds.当ilmenite里的iron被高度氧化之后,钻石也被氧化,所以钻石就变得很少了。所以这题C更合理。

2015-01-06 07:26:32  IP属地:局域网
妮妮酱923

妮妮酱923

应该是的,相比来说C更好

2014-01-09 15:01:26  IP属地:上海
wulianxt

wulianxt

错选B,看来是absence的问题....

2014-11-07 11:25:34  IP属地:北京
hjikod

hjikod

B选项不是因为ilmenites的出现表明了the absence of diamonds, 而是因为when the iron in ilmenite was highly oxidized, its source pipe rarely contained any diamonds 和 when iron became highly oxidized, so did diamonds.当ilmenite里的iron被高度氧化之后,钻石也被氧化,所以钻石就变得很少了。
所以这题C更合理。

2015-01-05 03:37:49  IP属地:局域网
leopoldchang

leopoldchang

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.

2013-05-03 01:05:34  IP属地:局域网

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