被CXD的一道逻辑题给难倒了，请大N们帮忙解释解释吧

题目：

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 protrait now seen on the surface of the canvas. Because the face of the woman in the underimage also appear 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 properly drawn if which of the following is assumed?

A, If the 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 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.

D, A painted canvas cannot be reliably attributed to an artist unless the authenticity of any underimage that painting might contain can 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 paiting is performed.

答案是C，我真是有些搞不懂，希望那位高人给我指点，解释一下。谢谢喽！

Hi, lguo1, thank you so much for your detailed explanation, it makes me feel more clear now. Regarding to your question, actually I don't know where it's available for downloading, I just bought this book, and it cost about 30rmb.

Thanks again for your great help!  

D the authenticity of any underimage that painting might contain can reliably attributed to the artist 是 “A painted canvas can be reliably attributed to an artist”的必要但不充分条件。

E “reliable X-ray examination of the paiting is performed”是A painted canvas can be reliably attributed to an artist” 必要但不充分条件 

A：不相关。

B：既不必要也不充分条件

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。 ” since we know the recently discovered painting contains an underimage of a woman also appears on van Gogh's painting, so the recently discovered painting is not incorrectly attributed to van Gogh, in other words, the recently discovered painting was painted by van Gogh.