@RachelSalisbury Additionally, in the explanation video, it says the the issue at hand is whether the museum director obtained the appropriate price for the pieces. But this is never mentioned as the critics' concern. The critics are concerned that the museum has violated its duty as a trustee of art for future generations by selling the pieces AT ALL, regardless of the price at which they are sold. Therefore what's at issue is not whether the sale price was fair, but whether the pieces constitute 'first-rate pieces' which would mean that their sale AT ANY PRICE is a loss to the museum.

Evaluating Option E further: It bases its conclusion {the fact that the price reflects that the pieces are first rate} on facts that could, in the given situation, have resulted from causes other than those presupposed by the argument.

I could see Option E being true if you argue that the high re-sale price of the pieces is caused by something other than the pieces being first-rate; for example, you could say that the pieces are being re-sold at a high value for a reason other than the 'first-rate-ness' of the piece (for example, the pieces could be reselling at a higher value because of the publicity around the controversy of the sale from the museum).

I interpreted Option A completely differently than how it was interpreted (and then rejected) in the explanation.

It concludes that a certain opinion [the opinion held by the critics, that the museum lost a first rate piece] is correct on the grounds that it is held by more people than hold the opposing view.

I interpreted it this way: The conclusion of the passage is that the price at which the piece was resold settles the issue that the critics were correct that the piece was first-rate; the price is the aggregate of the opinion held by everyone participating in the market for these paintings. The passage says that the fact that the art market in general valued the piece at a higher price than it was sold for (i.e., the market found the piece to be 'first-rate') demonstrates that the critics were indeed correct that it was first rate, and as a result, that it's sale was a loss for the museum. The passage is then vulnerable to the criticism that it is not the market that decides what is first rate; this can be restated as "a certain opinion is not necessarily correct based on the fact that the general market reflects that it is correct," which is a restatement of Option A. You could argue that the museum director's experience or skill positions him to have more on an authority on what is first rate, or what is a loss to the museum's collection, than the critics and/or the market.

The explanation video represents Option A as a statement about the number of critics versus the singular museum director. But the actual conclusion is the passage is about the price determined by the market versus the evaluation of the critics/museum director, and this would still be a consensus versus individual(s) argument even if there were only one critic.

Could someone please indicate where I've gone wrong in my reasoning.

The last example is a bit sloppy. It is not correct to include the phrase "is wrong" in the last example as a negative referential just because it negates the former statement. There is a hidden or implied referential in the sentence ("But he is wrong about that.") where "that" is the referential, and it is not a negative referential. The fact that the content of the predicate is such that the author is negating the previous sentence does not make that predicate referential; instead, the referential is inferred.

This becomes clearer if you remove the first referential: "One prominent biologist, Dr. H, hypothesized that the colors function as camouflage. But Dr. H is wrong." There are no words in these sentences serving grammatically as a referential, although you can imply from context that the thing he is wrong about is the hypothesis.