请问GWD27-12（黑洞）选B还是A?

eng_mba

给的答案是A,我觉得是B,看了以前的帖子，也有很多人说B, 不知道最后答案是什么,

麻烦NN指点，多谢了！

GWD27-Q10 to Q12:

 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.

--------------------------------------------------------------------------------

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?

                       

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

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.

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

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

5. 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.

Answer:

l980053

A.根据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……可以知道 NGC 4258 和第一段的例子是一样的,然后最后一句

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. ，可以知道要削弱结论，只要将其取非。既里面的星并不会撕裂the cluster

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. ，可以知道要削弱结论，只要将其取非。既里面的星并不会撕裂the cluster

eng_mba

可是原文要削弱的是第一段的最后一句话，不是第二段的结论呀。

第一段最后一句说cluster可能是原因，要削弱不是要证明cluser不能是原因吗？

迷茫中。。。

l980053

The same hypothesis might have

been applied to the galaxy NGC 4258, 这句话说明了第一段的结论同样适应NGC 4258这个例子。我上面不已经指出来了吗？？

 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.

削弱这句的话就是削弱IF……，THEN，对立面就是IF……，THEN NOT……。这正好是答案A。

chamcham

totally confused I thought the non-BL hypothesis cant not apply to NGC 4258 with the reason mentioned in NO. 2 paragraph. So as Q12, if we want to weaken the non-BL hypothesis's application on M87, we should also use the same reason in No. 2 paragraph, NOT the converse reason !!!

Vote for B.

chamcham

I saw it on May JJ, the answer is B

tendgrr

我原来也选B, 但是再仔细看了一下题，undermine the possible explanation，要削弱的是对这一现象的解释，而非这一现象，所以A对

chuneyu_lee

我支持本题选B。

l980053说文章中有：

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.

答案为对上面这段取非，所以选A。这个请l980053再考虑一下：本章原本是做虚拟语气，说明作者想表达的意思是：因为conllisions 没有torn the cluster part，所以ngc 4258不是a star cluster。而这个事实正是作者用来undermine第一段最后的skeptics所提出的解释的。所以A与作者的意思相反，应该为加强skeptics所提出的解释的。

    我支持本题选B，它是原文中上面一段话的改写。

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.

答案为对上面这段取非，所以选A。这个请l980053再考虑一下：本章原本是做虚拟语气，说明作者想表达的意思是：因为conllisions 没有torn the cluster part，所以ngc 4258不是a star cluster。而这个事实正是作者用来undermine第一段最后的skeptics所提出的解释的。所以A与作者的意思相反，应该为加强skeptics所提出的解释的。

    我支持本题选B，它是原文中上面一段话的改写。

o_c_01

以下是引用tendgrr在2007-6-24 21:10:00的发言：
我原来也选B, 但是再仔细看了一下题，undermine the possible explanation，要削弱的是对这一现象的解释，而非这一现象，所以A对

恩~~但是a好像也并没有undermine哪个现象的解释~~~~~~~

foreverluke

也许C是最好的答案，因为NGC 4258 等即使排列更紧密，实际上也被说明不可能作为旋转的中心引力，那么排列更松弛的M87更不可能了