Critical Reasoning

Serious individual art collectors are usually discreet when making significant purchases or sales related to their collections. At art auctions, for example, these collectors often place anonymous bids for major artwork. Therefore, the whereabouts of most of the world's most valuable artwork is probably unknown.

Each of the following, if true, would weaken the conclusion above EXCEPT:

A. The value of a piece of art is purely subjective.
B. Serious art collectors usually publicize their new artwork several months after making a purchase.
C. Museums own the vast majority of the world's most valuable artwork.
D. Of all the individuals in the world who own extremely valuable artwork, only a few are considered serious art collectors.
E. The private collections of most serious individual art collectors are often displayed in public settings.

OA to follow after some discussion !!

IMO: D is the correct answer. I have some doubts about A. Anyway I would choose D as the correct answer.