【OG24-614题】The discovery of which of the following would call into question the conclusion 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 discovery of which of the following would call into question the conclusion mentioned ?(highlight)

An asteroid 100 meters in diameter rotating at a rate of once per week An asteroid 150 meters in diameter rotating at a rate of 20 times per hour An asteroid 250 meters in diameter rotating at a rate of once per week An asteroid 500 meters in diameter rotating at a rate of once per hour An asteroid 1, 000 meters in diameter rotating at a rate of once every 24hours

正确答案： D

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文章大意逻辑
文章探讨小行星的结构，先说明小行星碰撞对旋转速度的影响：若为独石，旋转速率图应呈钟形分布；若为碎石堆，快速旋转的尾部会缺失。接着给出研究发现：除5个外，观测到的小行星都遵循旋转速率严格限制，直径超200米的有突变。得出结论：直径超200米的小行星是多组件结构或碎石堆，这与计算机模拟相符，还解释了大、小天体结构差异的原因，大天体因碰撞常成碎石堆，小天体多为独石。 文章类型及逻辑简图
文章类型为观点论证型。逻辑简图： Asteroid collision effect on rotation rate: monolith bell shaped distribution; rubble piles missing fast rotator tail Research discovery: almost all asteroids obey rotation rate limit, cutoff for > 200 meter asteroids Conclusion: > 200 meter asteroids are rubble piles, consistent with simulation, reason for large/small asteroid structure difference 做题方法及问题类型
问题类型为削弱论证题。做题方法是根据文章得出的结论“直径超过200米的小行星是多组件结构或碎石堆”，找出能对该结论产生质疑的选项，定位到结论相关描述及对碎石堆和独石旋转特性的阐述。 选项分析
A选项：直径100米的小行星，一周旋转一次。直径小于200米，属于小天体，其旋转情况与结论讨论的大天体结构无关，不能削弱，排除。 B选项：直径150米的小行星，每小时旋转20次。同样是小天体，与结论所针对的大天体结构无直接关联，不能削弱，排除。 C选项：直径250米的小行星，一周旋转一次。虽然直径大于200米，但旋转速度慢，不能有力质疑其是碎石堆结构，排除。 D选项：直径500米的小行星，每小时旋转一次。按照结论，大天体是碎石堆结构旋转速度不能太快，此选项中该大天体旋转速度快，说明可能不是碎石堆结构，对结论构成质疑，当选。 E选项：直径1000米的小行星，每24小时旋转一次。旋转速度慢，符合碎石堆结构特点，是对结论的支持而非削弱，排除。

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