还没有登录哦！
[Reading Comprehension]
试题详情
文章：
| Line | 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 | |
| (5) | 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 | |
| (10) | 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 | |
| (15) | 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 | |
| (20) | 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 | |
| (25) | 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 | |
| (30) | or increases slightly. This unexpected result |
| indicates that the falloff in luminous mass with | |
| #160; | distance from the center is balanced by an |
| increase in nonluminous mass. | |
| Our findings suggest that as much as 90 percent | |
| (35) | of the mass of the universe is not radiating at any |
| wavelength with enough intensity to be detected | |
| on the Earth. 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 | |
| (40) | 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. |
题目：
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
选项:
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
答案:
D
提问：
我当时的做题思路： 定位到24--26行 ,知道rotational velocity随者离中心越来越远 也越来越少 排除ADE---剩下BC ---22--24行 说L这个东西离中心越远 越少 ---选 A 看到答案 我看原文 发现27行有一个instead 转折 答案应该是它后面内容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 falloff in luminous mass with distance from the center is balanced by anincrease in nonluminous mass. 其中 This unexpected result indicates that the falloff in luminous mass with distance from the center is balanced by anincrease in nonluminous mass.这句话老师能不能解释一下 我不太理解 我不知道我看完答案后我的想法是不是对的， 但是instead 后面的内容说的是关于spiral galaxies，并没有说 the region just outside the nucleus 希望老师可以讲解一下这道题 谢谢
解答：
点赞0
阅读605
提问：
我当时的做题思路： 定位到24--26行 ,知道rotational velocity随者离中心越来越远 也越来越少 排除ADE---剩下BC ---22--24行 说L这个东西离中心越远 越少 ---选 A 看到答案 我看原文 发现27行有一个instead 转折 答案应该是它后面内容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 falloff in luminous mass with distance from the center is balanced by anincrease in nonluminous mass. 其中 This unexpected result indicates that the falloff in luminous mass with distance from the center is balanced by anincrease in nonluminous mass.这句话老师能不能解释一下 我不太理解 我不知道我看完答案后我的想法是不是对的， 但是instead 后面的内容说的是关于spiral galaxies，并没有说 the region just outside the nucleus 希望老师可以讲解一下这道题 谢谢
解答：
点赞0
阅读606
问个问题
注册太麻烦？点这里查看免费答疑吧！
博币不足
加"GMAT小百科"小智微信
直接送200
