悦度进来看一下：GWD24-17-Q10 to Q12-Q12

dq81

这道题12题答案是B，我有些不明白，有看过的童鞋一起讨论下why吗？
GWD27-Q10 to Q12:

Astronomers theorize that a black hole forms when a massive object shrinks catastrophically under its own gravity, leaving only a gravitational field so strong that nothing escapes it. Astronomers must infer the existence of black holes, which are invisible, from their gravitational influence on the visible bodies surrounding them. For example, observations indicate that gas clouds in galaxy M87 are whirling unusually fast about the galaxy’s center. Most astronomersbelieve that the large concentration of mass at the galaxy’s center is a black hole whose gravity is causing the gas to whirl. A few skeptics have argued that the concentration of mass necessary to explain the speed of the whirling gas is not necessarily a black hole: the concentration in M87 might be a cluster of a billion or so dim stars.

The same hypothesis might have been applied to the galaxy NGC 4258, but the notion of such a cluster’s existing in NGC 4258 was severely undermined when astronomers measured the speed of a ring of dust and gas rotating close to the galaxy’s center. From its speed, they calculated that the core’s density is more than 40 times the density estimated for any other galaxy.If the center of NGC 4258 were a star cluster, the stars would be so closely spaced that collisions between individual stars would have long ago torn the cluster apart.
Q12: Which of the following, if true, would most clearly undermine the possible explanation for the whirling gas in M87 that is mentioned in the last sentence of the first paragraph?
A.The stars in a star cluster at the center of M87 could exert a strong gravitational force without tearing the cluster apart.

B.A cluster of stars at the center would preclude the existence of certain other astronomical phenomena that have been observed at the center of M87.

C.The stars within many existing galaxies, such as NGC 4258, are more closely spaced than are the stars within the core of M87.

D.Only one other galaxy has been observed to contain gas clouds whirling about its center as they do about the core of M87.

E.The gravitational force of a cluster of a billion or so dim stars would be sufficient to cause a whirling ring of gas and dust to collect around the center of a galaxy

ruirui_hsu

同问此题。我选的C

hwwxhxx

up

兰心寒

挖个坟，记录下自己的看法。
C是支持而非削弱的。因为全篇关于skeptics和most astronomers的观点争议之处在于，那坨concentration of mass到底是什么？most astronomoers认为是黑洞（作者也隐含支持），skeptics认为是dim stars。
回到这题，问怎样削弱skeptics的观点。
先看B，a cluster of stars ... would preclude the existence of ...（直接否认stars的合理性）
再看C，the stars within many existing galaxies ... are more closely spaced than are the stars within the core of M87(天哪，看到了吗，用的一般现在时，这不是承认star已经存在了吗？这不是支持了skeptics的观点吗？）