GMAT阅读OG文章解析!GMAT阅读复习中，大家可以多利用OG资料来进行复习。对于一些比较难的阅读文章和题目，大家可以参考一下相关的答案解析，来解答心中的疑惑。下面小编为大家整理了详细的内容，供大家参考!
After evidence was obtained in the 1920s that the universe is expanding, it became reasonable to ask: Will the universe continue to expand indefinitely, or is there enough mass in it for the mutual attraction of its constituents to bring this expansion to a halt? It can be calculated that the critical density of matter needed to brake the expansion and "close" the universe is equivalent to three hydrogen atoms per cubic meter. But the density of the observable universe—luminous matter in the form of galaxies—comes to only a fraction of this. If the expansion of the universe is to stop, there must be enough invisible matter in the universe to exceed the luminous matter in density by a factor of roughly 70.
Our contribution to the search for this "missing matter" has been to study the rotational velocity of galaxies at various distances from their center of rotation. It has been known for some time that outside the bright nucleus of a typical spiral galaxy luminosity falls off rapidly with distance from the center. If luminosity were a true indicator of mass, most of the mass would be concentrated toward the center. Outside the nucleus the rotational velocity would decrease geometrically with distance from the center, in conformity with Kepler's law. Instead we have found that the rotational velocity in spiral galaxies either remains constant with increasing distance from the center or increases slightly. This unexpected result indicates that the fall off in luminous mass with distance from the center is balanced by an increase in nonluminous mass.
Our findings suggest that as much as 90 percent of the mass of the universe is not radiating at any wavelength with enough intensity to be detected on the Earth. [Line 34-37] Such dark matter could be in the form of extremely dim stars of low mass, of large planets like Jupiter, or of black holes, either small or massive. While it has not yet been determined whether this mass is sufficient to close the universe, some physicists consider it significant that estimates are converging on the critical value.
Questions 115-119 refer to the passage above.
115. The passage is primarily concerned with
A. defending a controversial approach
B. criticizing an accepted view
C. summarizing research findings
D. contrasting competing theories
E. describing an innovative technique
116. The authors' study indicates that, in comparison with the outermost regions of a typical spiral galaxy, the region just outside the nucleus can be characterized as having
A. higher rotational velocity and higher luminosity
B. lower rotational velocity and higher luminosity
C. lower rotational velocity and lower luminosity
D. similar rotational velocity and higher luminosity
E. similar rotational velocity and similar luminosity
117. The authors' suggestion that "as much as 90 percent of the mass of the universe is not radiating at any wavelength with enough intensity to be detected on the Earth" (lines 34-37) would be most weakened if which of the following were discovered to be true?
A. Spiral galaxies are less common than types of galaxies that contain little nonluminous matter.
B. Luminous and nonluminous matter are composed of the same basic elements.
C. The bright nucleus of a typical spiral galaxy also contains some nonluminous matter.
D. The density of the observable universe is greater than most previous estimates have suggested.
E. Some galaxies do not rotate or rotate too slowly for their rotational velocity to be measured.
118. It can be inferred from information presented in the passage that if the density of the universe were equivalent to significantly less than three hydrogen atoms per cubic meter, which of the following would be true as a consequence?
A. Luminosity would be a true indicator of mass.
B. Different regions in spiral galaxies would rotate at the same velocity.
C. The universe would continue to expand indefinitely.
D. The density of the invisible matter in the universe would have to be more than 70 times the density of the luminous matter.
E. More of the invisible matter in spiral galaxies would have to be located in their nuclei than in their outer regions.
119. The authors propose all of the following as possibly contributing to the "missing matter" in spiral galaxies EXCEPT
A. massive black holes
B. small black holes
C. small, dim stars
D. massive stars
E. large planets
题材：Astronomy
类型：现象解释
框架：explaining universe, dark matter
主旨：对宇宙终结问题的质疑
P1(提出问题)：宇宙的扩张是否会停止?这与宇宙整体质量有关。物质密度临界值是可以计算的，只是它不全面，没有包括不发光物质。
P2(解决问题)：对不发光物质的研究:研究发现虽然发光物质随离中心的距离数量减少但自转速度不变，推知不发光物质的量是随距离增多的。
P3(问题的进展)：不发光物质占宇宙90%。这些不发光物质的量是否足够停止宇宙扩张需要临界值的进一步精确。
逻辑链：
1、提出问题，给出计算答案
2、解释问题，给出结论
3、无法确定，科学家推测
题目类型：115：主旨 116：细节信息 117：逻辑 118：细节推断 119：细节信息
解题定位(根据OG13解释)：
115：根据全文框架发现此文是一个现象解释
116：难题，因为这里考到专业解释的地方了，而且有对比，必须读懂。看选项就知道要对比2个地方，一个是明亮度，一个是转速。亮度定位到Line20-21：亮度随着距离变大而下降，所以outside比outermost亮度要高。转速定位到Line27-30：速度随着距离变化不大。所以outside比起outermost是相似的
117：文章用典型螺旋星系的例子来说明主题，想削弱，可以说样板不具备代表性，就是说如果这个螺旋星系是非典型的即可
118：根据问题定位到Line7-9，这句话是一个总结，问题的意思说如果密度达不到会发生什么，那么选项和这个总结相反就可以
119：定位Line37-40，排除文中没提到的即可
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