Trouble deciding between C vs. E

Hello there, happy to help! You are correct! We learn that exposing structural materials "called for an unrealistically high level of craftsmanship" (lines 50 to 53). However, we do not learn anything about builders' willingness, or lack thereof, to attempt this. Support for answer choice (E) can be found following the introduction of the ideal of exposing structural materials as well as before. Lines 31 to 36 tell us that the Modern Movement declined "partly as a result of Modernist architects' ignorance of building methods, and partly because Modernist architects were reluctant to admit that their concerns were chiefly aesthetic." This ignorance of building methods is not practical, and the passage concedes that these architects' concerns were primarily aesthetic. Additionally, we learn in lines 50 to 60 that this ideal "called for an unrealistically high level of craftsmanship," was "prohibitively expensive," and "imposed unnecessary limitations on building design." Choosing to continue to pursue this ideal in the face of such limitations suggest that the architects were not focused on practical concerns, but rather continued to pursue this ideal as an aesthetic choice. Hope this helps! Please let us know if you have any further questions.