Principle questions like this are so challenging because they require us to think about the argument in abstract terms. So, let's try that.
The author disagrees with those who think that those who critique the agglomeration of masterpieces in cities on two grounds. First, they think it would be impractical to distribute them wider, and second because such works benefit from the network effect of being close to other great works.
C does not really get to either of the authors points. While c could support the author directionally, this would require a couple of assumptions on our part. We would need to assume that this is in fact a redistribution of social goods (as opposed to merely stopping further masterpieces from being moved to cities), and it does not seem that urbanites would actually be deprived. The author appears to concede that there are a wealth of masterpieces in cities already, so up to a point, removing some would not lead to deprivation.
D is more on the nose. It directly strengthens the authors argument about what is practical.
