Leela,
I am going to quote part of Adam's response because it is exactly right.
But there's another, even better reason to reject answer D and select answer E here, and that is because it is completely clear from the entire Main Point and Tone of the passage, and the author's stated Viewpoint, that the author does NOT believe those artists were predicting social changes. That's the whole thing he is arguing against! Answer D may be a little vague, but answer E is a slam dunk for being the best of the bunch. If you aren't sure about one answer, but sure another is correct, go with the one you are sure about!
In a way, this is a global question (authors tone/main point) disguised as a local question (specific reference). We need to understand what the author is arguing for and against. The essential set up of this passage is that the author is arguing against an extreme critic who says that artists are valuable only for how they anticipate or predict political events and not for their artistic achievement. The author strongly disagrees. So, the author would NEVER EVER agree with E, that the painters works contained an example of the power to predict social change. Yes, the passage does talk about it, but only to reject and attack that idea.
Another way to think about it is to rephrase the question: "Why does the author think the works of the pre-war painters are important? ABCD all fit, but definitely not E. That is the whole point of the passage.