Hi avengingangel - let me see if I can help you out!
E is correct based of the final lines of the passage, where we’re told that when “photography preempted painting as the means of obtaining portraits [i.e. portraiture became less common/popular], painters had more freedom to vary their subject matter.” That’s exactly what E gives us: when painters were painting fewer portraits (due to photos’ increased usage), painters could move beyond literal depictions (conventional portraits) and explore non-literal (abstract) depictions.
B, on the other hand, is wrong for at least two reasons: first, it’s too broad in saying “the nineteenth-century
knowledge of light and movement provided by photography,” since all we know is that some Impressionist artists studied
elements of light and movement in photos, and their “knowledge” wasn’t about light/movement itself but rather about how they show that our perceptions can distort reality—that’s not the same as gaining insight into the true nature of light and movement; second, and more critically, saying that that knowledge “inspired the abstract works characteristic of modern art” is wayyy too strong when all we know is that Degas and perhaps only a few others (“Impressionist artists like Degas”) paid any attention to this aspect of photography. We certainly can’t know that the study by a handful of people was the inspiration for [all] modern arts’ abstract characteristics.
As for the use of "preempt(ed)" it's consistent here. In both cases--"artistic efforts achieved with machines preempt human creativity," and "photography preempted painting as the means of obtaining portraits"--it means to prevent or take the place of, two entirely acceptable usages. In the former it's used to suggest that machines hamper/subvert human creativity; in the latter it's used to indicate photography replaced painting as the main means of making portraits. If you look up "preempt" you'll see both as part of its definition
I hope that helps!
Jon Denning
PowerScore Test Preparation
Follow me on Twitter at
https://twitter.com/jonmdenning
My LSAT Articles:
http://blog.powerscore.com/lsat/author/jon-denning