【OG24-613题】The passage implies which of the following about the five asteroids mentioned? (highlight)_mofa留学圈mofaGRE在线题库系统_GRE在线搜题_GRE题库解析_GRE真题机经_GRE课程_GRE培训机构

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When asteroids collide, some collisions cause an asteroid to spin faster ; others slow it down. If asteroids are all monoliths---single rocks---undergoing random collisions, a graph of their rotation rates should show a bell-shaped distribution with statistical "tails" of very fast and very slow rotators. If asteroids are rubble piles, however, the tail representing the very fast rotators would be missing, because any loose aggregate spinning faster than once every few hours (depending on the asteroid's bulk density) would fly apart. Researchers have discovered that all but five observed asteroids obey a strict limit on rate of rotation. The exceptions are all smaller than 200 meters in diameter, with an abrupt cutoff for asteroids larger than that.

The evident conclusion---that asteroids larger than 200 meters across are multicomponent structures or rubble piles---agrees with recent computer modeling of collisions, which also finds a transition at that diameter. A collision can blast a large asteroid to bits, but after the collision those bits will usually move slower than their mutual escape velocity. Over several hours, gravity will reassemble all but the fastest pieces into a rubble pile. Because collisions among asteroids are relatively frequent, most large bodies have already suffered this fate. Conversely, most small asteroids should be monolithic,because impact fragments easily escape their feeble gravity.

The passage implies which of the following about the five asteroids mentioned? (highlight)

Their rotation rates are approximately the same. They have undergone approximately the same number of collisions. They are monoliths. They are composed of fragments that have escaped the gravity of larger asteroids. They were detected only recently.

正确答案： C

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文章大意逻辑
文章探讨小行星的结构。首先提出小行星碰撞会使旋转速度改变，若为独石（monoliths），旋转速率图是钟形分布；若是碎石堆（rubble piles），快速旋转的尾部会缺失。接着指出研究者发现除了五颗小行星外，其他都遵循旋转速率严格限制，这五颗直径小于200米，大于此直径有明显截断。最后得出结论：直径大于200米的小行星是多组件结构或碎石堆，这与计算机模拟碰撞结果相符，还解释了大小行星结构不同的原因。 文章类型及逻辑简图
文章类型：观点论证型。逻辑简图： Collisions affect asteroids' spin rates. Monoliths: bell shaped rotation rate distribution. Rubble piles: no fast rotator tail. Exception of five asteroids in rotation rate limit. Conclusion: asteroids > 200m are rubble piles/multicomponent structures. Computer modeling supports. Explanation of monolithic and rubble pile structures for different sized asteroids. 问题类型及做题方法
问题类型：推断题。做题方法：根据文中关于五颗小行星的描述以及整体对小行星结构和旋转速率的讨论进行推断。定位提示句子为“Researchers have discovered that all but five observed asteroids obey a strict limit on rate of rotation. The exceptions are all smaller than 200 meters in diameter, with an abrupt cutoff for asteroids larger than that.” 选项分析
A选项：文中未提及这五颗小行星旋转速率大致相同，属于无中生有，排除。 B选项：文章没有任何信息表明它们经历了大致相同数量的碰撞，排除。 C选项：文中说大部分小的小行星应该是独石（monolithic），这五颗直径小于200米，属于小的小行星，所以推断它们是独石，该项正确。 D选项：文中没有提到它们是由逃离较大小行星引力的碎片组成，排除。 E选项：文中没有提及它们是最近才被发现的，排除。

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