I agree with christoph
and IMO option A is more pertinent here as compared with B because in B the words "outweighed by" aren't correct and imply as if the pollution (negative aspect) is dominating over or surpassing the financial benefits (desirable outcome) WHEREAS the correct lingo should have mentioned that the pollution (negative aspect) OUTWEIGHS the financial benefits (desirable outcome) obtained by using the snowmobiles .Moreover, the environmentalist argues that the financial benefits as such can be obtained ( although degree of the benefit isn't known) through inviting the skiers by reducing the sound and noise pollution by use of snowmobiles. Other members, please provide your opinions regarding this.
OA is definitely B.
Reading your post, I think you have it backwards. Let's break down the argument, B, and then A (and then a note on C):
1. The environmentalist is saying that the snowmobiles cause pollution.
2. The business spokesperson says that we should put up with the pollution because it generates revenue. Basically, that the benefits of the revenue outweigh the negatives of the pollution.
3. The environmentalist responds by pointing out that the pollution also causes a decrease in a different revenue stream, the one from the skiers.
Basically, the environmentalist is pointing out another consideration that argues against the business spokesperson's idea. Specifically, the environmentalist is saying that the snowmobile revenue does not overcome the negatives of the pollution because it is not just snowmobile revenue v. pollution, but rather snowmobile revenue v. both pollution and skier revenue. This doesn't necessarily mean that the skier revenue is definitely more than the snowmobile revenue (the environmentalist could believe it to be or believe it not to be); instead, it means that the difference between the snowmobile revenue and the skier revenue (if any) is not more than the negatives of the pollution. Thus, when we are asked how the environmentalist responds, we need an answer that says that the environmentalist argues against the idea that the negatives of pollution are outweighed by the benefits of the revenue, not one that says that the skier revenue is more than the snowmobile revenue - the more/outweigh issue in the argument is really about money v. pollution (this is important for answer C). One thing to notice about A and B is that they start with "challenging an assumption that", meaning that the remainder of those answers should match the business spokesperson's assumption (that the snowmobile revenue is the best option) since that is what the environmentalist challenges.
B: "Challenging an assumption that certain desirable outcome is outweighed by negative aspects associated with producing that outcome"
This answer tells us that the environmentalist is challenging the business spokesperson's assumption that a certain desirable outcome (maybe stopping the pollution) is outweighed by (not as good as) negative aspects associated with producing that outcome (maybe the lost snowmobile revenue). This fits exactly what we want because the environmentalist is saying that the business spokesperson is wrong for thinking that we shouldn't clean up pollution because of the money. I think you flipped this instead. Maybe you focused on the "desirable outcome" as instead being the snowmobile revenue? Maybe you missed the "challenging" word at the beginning and thought that it meant that the environmentalist believes in that assumption? Be careful when you read that you have everything in the right order. Slowing down and rechecking your thoughts can often lead to clarity.
A: "Challenging an assumption that certain desirable outcome can derive from only one set of circumstances"
What is the "desirable outcome" here? It definitely cannot be stopping the pollution because we are not talking about accomplishing stopping the pollution in "other" ways. Instead, the desirable outcome here would have to be keeping the snowmobile revenue (so this would have to be a different desirable outcome from the one in B). Thus, this answer would have to be saying that the environmentalist is arguing against the idea that the snowmobile revenue can come from only one set of circumstances.
That we are talking about other sources of revenue makes this very attractive, but the word "only" is extremely important here ("only" isn't always wrong, but you should always evaluate how it affects things!). With "only", this answer tells us that the environmentalist is saying that business spokesperson wrongly thinks that the snowmobile revenue cannot come from other sources. This doesn't match because, while the environmentalist is telling us that revenue can come from other sources, the business spokesperson never says that we cannot get money from other sources. This is the key here. It is entirely consistent with the business spokesperson's position that the business spokesperson thinks that there are other ways to make money (maybe a coffee stand?). So, the environmentalist is not arguing against the snowmobile revenue being the "only" way to achieve that outcome; instead, the environmentalist is telling us that the business spokesperson is wrong because the skier revenue would be lost too, so all of a sudden maybe the negative aspects of banning snowmobiles (lost revenue) isn't outweighing the pollution - maybe instead the skier revenue makes it a closer situation and the pollution is bad enough to lose a small amount of money. Thus the argument is more about which option is better, not whether something is the only option, meaning that A cannot be correct.
C: "Maintaining that the benefit that the spokesperson desires could be achieved in greater degree by a different means."
This sounds really close, because the environmentalist seems to suggest that there is a benefit that the spokesperson desires (snowmobile revenue) that we could get "in greater degree by a different means" (from the skiers), but it doesn't match as well for a few reasons. First, "maintaining" is a little too strong here. It suggests that the speaker has already said that this is true. If I say A is true and you say B is true and then I say A is still true, then I maintained my position. Instead, the environmentalist never began by discussing the financial benefits and so cannot "maintain" that position. Much more importantly, the author never actually says that we can get more money from skiers, it is only suggested. The problem with that is it is entirely possible and consistent with the argument that the lost snowmobile revenue (say $10,000) is more than the lost skier revenue (say $9,000) and that the difference ($1,000) is not enough to justify putting up with the pollution. Thus, the environmentalist doesn't have to believe that the monetary benefit could be achieved in a greater degree (more money) by another means (skier revenue); instead, the environmentalist is saying that the skier revenue makes it okay to stop the pollution and lose the snowmobile revenue. This is different than B because B just says that one situation is outweighed by another, while C says that a specific benefit must be able to be achieved to a greater extent through another means and we don't know that that is true.
fguardini1, Aristocrat, and nerd got pretty close to explaining it correctly a few posts above - I just wanted to expound to, hopefully, make it very clear