@KevinLin I understand why you feel that the original comment was uncharitable, so I do apologize. That specific part wasn't meant very seriously -- I don't actually think tutors or anyone else are "pretending" anything. It was mostly a rhetorical gesture, in the same way that saying AC A is the worst "correct" answer ever was rhetorical. I think what I was trying to say was something like "It's so impossible to actually defend AC A, they must just be gritting their teeth and pretending their best on this one, because what else can they do? They didn't write the test, but they have to come up with some explanation of why this answer is the right one." I wouldn't use rhetoric like that (saying someone is "pretending") in any actual back-and-forth with any specific person, but I can definitely see how my original comment, which wasn't addressed to anyone in particular, could still be seen as an unfair characterizing of "7Sage writers and tutors". (added this edit after initial posting)

I do agree that it is most productive, even when this test is very frustrating, to understand the best possible arguments in favor of the correct answer. I've usually found even with very difficult questions, I can eventually come around and accept those best arguments. This question stood out among all others I've ever encountered as truly straining my ability to do that, hence the rhetoric.

I'll try to respond to the rest of your reply when I have the chance to review it carefully.

@KevinLin In general an author doesn't need to; but in this case, the author would need to in order to overcome everything else in the paragraph that signals endorsement.

While it's true that the sentence at the beginning of the second paragraph could, in isolation, indicate that what follows is not the actual view of the author, it doesn't necessarily have to indicate that. One could say "Here is one natural and obvious way of reasoning" and then offer a line of reasoning that one fully endorses (and more importantly, signal in that line of reasoning that they endorse it). This is where the rest of the paragraph becomes important. It's not reasonable to interpret that single sentence as indicating "I don't necessarily endorse this" based on what is found in the rest of the paragraph. Or, it would only be reasonable to do so if, for instance, the entire line of reasoning were in quotation marks, or some other similar signal of separation were offered.

Additionally, the official 7Sage explanation given for AC A is contradictory. The explanation says "...the author describes a line of reasoning without necessarily adopting it as her own". But then the explanation states that the sentence beginning with "This may be impractical" signals that the author doesn't necessarily agree with the argument. But "This may be impractical" is an essential part of that very argument that the author supposedly might not agree with. Rhetorically, acknowledging that the course of action "may be impractical [and] compromises might have to be made" is a key move in the argument; it sets up the final sentence, in which it is argued that, despite these impracticalities, this course of action is the best.

The 7Sage explanation depends on treating everything after the first sentence of the second paragraph as "the argument" that is not necessarily to be attributed to the author. But it then uses something from that "argument" ("This may be impractical") and attributes it to the author.

This has to be the worst "correct" answer choice I have ever seen. I feel sorry for the 7Sage writers and tutors having to pretend that the "This may be impractical..." sentence distances the author from the argument, when it actually obviously does the complete opposite.

The only way Answer Choice A would ever be correct is if the second paragraph ended with the following parenthetical: "(note: I am not necessarily personally endorsing this entire way of reasoning that I have just laid out in detail)".

I think the key word isn't just "if", it's also "could feed".

If that sentence were to read "So if steel-manufacturing plants fed the heat they produce into thermophotovoltaic generators...", then B would be a necessary assumption. In order for the plants to engage in this process in the first place, it would be necessary for the technology to actually exist for this process to happen.

I think the reason I got this wrong and chose B (even though I knew C "also" made sense as an answer) was because I didn't interpret "if...could feed" as meaning "if it was possible", creating a "hypothetical world" where it is possible. I misread it instead as meaning something like "if they bothered to".