[讨论]PREP1-15, 未讨论过的: B项如何排除?

15.        (26883-!-item-!-188;#058&002985)      

Astronomer: Observations of the Shoemaker-Levi comet on its collision course with Jupiter showed that the comet broke into fragments before entering Jupiter's atmosphere in 1994, but they did not show how big those fragments were.  In hopes of gaining some indication of the fragments' size, astronomers studied spectrographic analyses of Jupiter's outer atmosphere.  These analyses revealed unprecedented traces of sulfur after the fragments' entry. The fragments themselves almost certainly contained no sulfur, but many astronomers believe that the cloud layer below Jupiter's outer atmosphere does contain sulfur.  Since sulfur would have seeped into the outer atmosphere if comet fragments had penetrated this cloud layer, it is likely that some of the fragments were at least large enough to have passed through Jupiter's outer atmosphere without being burned up.

In the astronomer's argument, the two portions in boldface play which of the following roles?

(A) The first presents a circumstance for which the astronomer offers an explanation; the second is part of that explanation.

(B) The first acknowledges a consideration that weighs against the conclusion of the argument; the second is that conclusion.

(C) The first acknowledges a consideration that weighs against the conclusion of the argument; the second provides evidence in support of that conclusion.

(D) The first provides evidence in support of the conclusion of the argument; the second acknowledges a consideration that weighs against that conclusion.

(E) The first is a judgment advanced in support of the conclusion of the argument; the second is that conclusion.

先说一句, PREP里的这题其实跟GWD那道不同, 因为黑体字的部分是不一样的. 一鱼两吃, 各是各的味道.

PREP这题的答案是E. 我选的是B. 比较BE项, 区别在于对第一个BF部分的理解.

我不大明白为什么B不对, 试着理解如下:

原文要通过traces of sulfur的存在, 推出结论: 碎片足够大以致于可以穿透J星的外层大气而不被烧化. 第一处黑体排除了碎片本身带有sulfur的可能性.

如果把第一处BF取非, 碎片本身带有sulfur, 那么观察到的traces of sulfur有可能是碎片经过时留下的痕迹. 那么对于为什么会有traces of sulfur的解释会不同, 但是原文的结论同样也成立.

所以说B项说a consideration that weighs against the conclusion是不对的, 它只是weighs against the explanation.

不知道我这样理解对不对....请NN赐教.

首先确定文章结论是最后一句，所以答案在B和E。其次，BF第一部分与结论是统一的，所以不能选against，排除B，完毕。

同问，可否解释的具体些啊……3X~~~~