[求助]请教各位 大牛 大侠求解cxd假设题一道26

x-ray examination of a recently discovered painting- judged by some authorities to be a self-portrait by vincent van bogh- revealed an underimage of a woman's face.either van gogh or another painter coverd the first painting with the protrait now seen on the surface of the canvas. because the face of the woman in the 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 abobe is properly drawn if which of the following is assumed?

b many painted canvases that can be reliably attributed to van gogh contain underimages of subjects that appear on at least one other canvas that van 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

为什么b错c对呢？

d

because the face of the woman in the underimage also appears on canvases van gogh is known to have painted,<A>

the surface painting must be an authentic self-portrait by van gogh. <B>

b many painted canvases that can be reliably attributed to van gogh contain underimages of subjects that appear on at least one other canvas that van gogh is known to have painted.

b答案为什么不是1.让a可行?
            2有因有果,没有这个原因就没有这个结果.看意思确实能看出b不对 这归类对不对呢

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

c是notb>nota么 不过也存在错误呀 应该说所有不是梵高的画就都没出现过真品中出现的底影

B相当于必要——van gogh的paint确实有很多存在underimages

C相当于逆否——不是van gogh的paint就不存在underimage

条件型结论：结论带条件（即为充分必要）。ASSUMPTION的方法排除充分条件出现，必要条件不出现的情况。或充分条件一定能推出必要条件，或排除充分条件推不出必要条件的可能

这是lawyer中总结的话这题跟这个有关吧

看的不是太明白 哪位高人再帮忙解释下呗或告知哪能找到相关解释也行