请教GWD27-12

1.        GWD-27-Q10-Q12 黑洞存在的研究

Astronomers theorize that a black

       hole forms when a massive object

       shrinks catastrophically under its own

Line gravity, leaving only a gravitational

  (5)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.

 (10)For example, observations indicate

that gas clouds in galaxy M87 are

whirling unusually fast about the gal-

axy’s center.  Most astronomers

believe that the large concentration

 (15)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

 (20)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,

 (25)but the notion of such a cluster’s

existing in NGC 4258 was severely

undermined when astronomers mea-

sured the speed of a ring of dust and

gas rotating close to the galaxy’s

 (30)center.  From its speed, they calcu-

lated 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

 (35)stars would be so closely spaced

that collisions between individual

stars would have long ago torn the

cluster apart.

当然是a了，文章的最后一句话不是说得很清楚吗？这道题目是undermine，当然相反了

If the center of

NGC 4258 were a star cluster, the

 (35)stars would be so closely spaced

that collisions between individual

stars would have long ago torn the

cluster apart.

错误！

A说star之间的引力不足以分裂M87，完美支持了原文！ 和后文反例正好相反，负负=正！

选 B 觉得没有错

1. The stars in a star cluster at the center of M87 could exert a strong gravitational force without tearing the cluster apart.
               支持了原文

2. 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.
               如果是star，那么已经观察到的一些现象就不该出现，否定了。

vote for B~ no doubt