题目信息
I submit that impact of solid bodies is the most fundamental of all interstellar processes that have taken place on the terrestrial planets: without impact, Earth, Mars, Venus, and Mercury would not exist.
Simply put, the collision of smaller objects is the process by which the terrestrial planets were born. On the surface, that the geological record of the earliest history of impacts on the terrestrial planets has been lost, is troubling. As the process is self-erasing, to a certain extent, the earliest record would have been lost even if processes of melting and internal evolution of the planets had not occurred. But much of the record of the last stages of accretion of the planets is preserved, especially on the moon, Mercury, and Mars. In fact, the last stage of accretion is still going on, albeit at a very slow rate.
This is fortunate, because we can study many aspects of the processes of planetary birth by investigation of the nature of small bodies that still exist, the dynamics of their orbital evolution, and the effects that they produce when they ultimately collide with a planet. If impact and accretion were not still occurring, it would be hard to come to grips with a number of difficult problems of planetary origin and early evolution.
Simply put, the collision of smaller objects is the process by which the terrestrial planets were born. On the surface, that the geological record of the earliest history of impacts on the terrestrial planets has been lost, is troubling. As the process is self-erasing, to a certain extent, the earliest record would have been lost even if processes of melting and internal evolution of the planets had not occurred. But much of the record of the last stages of accretion of the planets is preserved, especially on the moon, Mercury, and Mars. In fact, the last stage of accretion is still going on, albeit at a very slow rate.
This is fortunate, because we can study many aspects of the processes of planetary birth by investigation of the nature of small bodies that still exist, the dynamics of their orbital evolution, and the effects that they produce when they ultimately collide with a planet. If impact and accretion were not still occurring, it would be hard to come to grips with a number of difficult problems of planetary origin and early evolution.
The primary purpose of the passage is to
A:present evidence that argues against a common misconception in the formation of planets
B:undermine a claim regarding the role accretion plays in planetary evolution
C:argue for the importance of using existing planetary conditions to understand prior cosmic occurrences
D:underscore the importance of an astronomical process and describe ways in which we can understand this process
E:discuss how, unless immediate action is taken, astronomers will squander an opportunity to better understand planetary formation
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已选答案：
正确答案：
D:underscore the importance of an astronomical process and describe ways in which we can understand this process
*内容概述：
文章开头说女性的草根运动时期和他们对新文明意识的看法的核心来自于美国在大推进时期的社会改革。接着进一步解释在这一时期中产白人女性改革者取得的成就。接下来笔锋一转，在童工问 题上不同阶级女性看法不同。改革者认为必须剔除，但工人阶级则认为童工法会让家庭里干活的人变少，生活难以为继。最后是作者的评价，承认改革者要求不适用童工是正确的，但他们没有考 虑到工人阶级的家庭经济状况
*文章类型：人文历史
*文章套路：对比解释说明
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*题目类型：主旨题
*选项分析：主旨题去看全文内容概述。本文的目的就是文章的结尾处说的中产阶级改革者没能够理解公认阶级的经济状况。因此正确答案是D
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