请教一道逻辑题

Caroline575104UID: 3655521

X-ray examination of a recently discovered painting- judged by some authorities to be a self-portrait by Vincent Van Gogh- revealed an underimage of a woman's face. Either van Gogh or another painter covered the first painting with the portrait now seen on the surface of the canvas. Because the face of the woman in underimage also appears on canvases van Gogh is known to have painted, the surface painting must be an authentic self-portrait by Van Gogh.
The conclusion above is probably drawn by if which of the following is assumed?
A. If a canvas already bears a painted image produced by an artist, a second artist who uses the canvas to produce a new painting tends to be influenced by the style of the first artist.
B. Many painted canvases that be reliably attributed to van Gogh contain underimages of subjects that appear on at least one other canvas that Gogh is known to have painted.
C. Any painted canvas incorrectly attributed to van Gogh would not contain an underimage of a subject that appears in authentic paintings by that artist.
D. A painted canvas cannot be reliably attributed to an artist unless the authenticity of any underimage that painting might contain can be reliably attributed to the artist.
E. A painted canvas cannot be reliably attributed to a particular artist unless a reliable x-ray examination of the painting is performed.
请问各位大神，这道题为什么选c啊，请说一下解题思路？我自己选的是D，不能理解C为什么对。
万分感谢！

wangli199547UID: 3595191

错在reliably？

Caroline575104UID: 3655521

wangli199547 发表于 2015-10-14 18:36
错在reliably？

谢谢你的回复

gterlannUID: 3595027

http://forum.chasedream.com/thread-460677-1-1.html

说真的这个题目非常难,我本来还觉得不符合GRE特点,但是突然发现是OG练习册V的阅读部分的最后一题;

这题的罕见之处在于对于assumption和逻辑的考察非常严厉,而并不是以前很多的ASP,把问题的CORE读出来基本就做对一半了;

首先文章的CORE还是要读:
有一幅画,有上层和下层两层;
下层画和梵高的其他画很像----------(assumption1)------------>下层画就是梵高画的--------
----(assumption2)-------->上层画也是梵高画的;

两个assumption叙述出来就是:
assumption1:如果下层画很像梵高的画,那么可以认为确实就是梵高画的;
assumption2:如果一幅画的下层画是梵高画的,那么上层画肯定就是梵高画的;

看题目,问的就是assumption;
看选项:
A:画家之间的互相影响与CORE无关;
B:这个考察的是第一个assumption,但是它并不是assumption1的完整逆反命题,assumption1的完整逆反命题应该是:every authentic van gogh contains a subject in his other works,而B选项用的是many,也就是一部分,并不能建立必要的逻辑关系;
C:这个其实就是assumption2的完整逆反命题:如果下层画是梵高画的,那么上层画就是梵高画的,当然整幅画也就是梵高画的;逆反过来就是:任何只要不是梵高画的画,那么它的下层画也不是梵高画的;
D:选项要表达的意思是,只有确定了下层画的作者,才能确定整幅画的作者;看起来这个很正确,但是要知道assumption在逻辑中对应的应该是充分条件,而D陈述的是一个必要条件,两者之间天差地别;
E:无关

这个题目总体还是很难的,也是我第一次在GRE ASP里碰到不使用逻辑取反就做不出来的问题;

Caroline575104UID: 3655521

gterlann 发表于 2015-10-19 13:26
http://forum.chasedream.com/thread-460677-1-1.html

说真的这个题目非常难,我本来还觉得不符合GRE特点 ...

C你分析的好对啊！那个逆反我觉得特别别扭，可是确实是这样的