Research has shown that shoppers who purchase garments in a "luxury"

You're completely correct--I think the post you were referencing accidentally took the counterposition to (A). As (A) stands, it is a good thing for sales of angora if the angora rabbit isn't threatened by the new disease. However, rather than acting as a real strengthener to the argument, (A) is actually an assumption. This difference is subtle, as assumptions do fundamentally support an argument, but essentially you can think of (A) as a prerequisite the conclusion's success (this must be true, or the conclusion will be in serious trouble) but not really as an active contributor to its success (because knowing that there are angora rabbits doesn't actually offer any evidence to support the contention that people will substitute angora for cashmere).

Now, why is B incorrect?

Option (B) falls victim to the same error as option (A). This new information is pretty important to the argument, as if the opposite is true--that people can tell the difference between cashmere and angora--then it casts doubt on the conclusion, which relies (again) on the idea that people will willingly substitute angora products for cashmere products. However, while knowing from (B) that the two materials are hard for most people to distinguish from one another makes this conclusion believable, it doesn't really help the conclusion as much as (D). For one thing, most people don't buy cashmere or angora, meaning that even if most people can't tell the difference, the minority of people who actually buy items made of these materials might still be able to distinguish between them. Also, even if we assume they can't practically tell the difference between cashmere and angora, that's not great evidence that they'll buy angora instead--it just opens up the possibility. So while it does somewhat help the conclusion, it's easy to conceive of an answer that does a better job.

Option (D) does that better job in two ways: it discusses buyers of luxury fabrics specifically, and it tells us that for those buyers, cashmere and angora occupy a similar niche. This makes it very believable that an increase in cashmere prices will push would-be cashmere buyers into buying angora and so positively supports the conclusion.

Hi carcass chetan2u mikemcgarry

Reason to eliminate B given in Magoosh's OA: People can confuse cashmere (C) with fake cashmere and buy ithe fake one more.. what? How can we even imply that? All we have been told that people cant tell the difference between 'cashmere (C) and angora (A)'. Also passage says that 'disease has significantly reduced the amount of C available on the market'

Doesn't customers 'not able to differentiate C and A
AND
C being less on the market'
DIRECTLY imply that people would purchase A more?

I am not saying that D is incorrect. I agree that if people have same reasons to buy both C and A, they might purchase A more in absence of C.
But B says 'most' and D doesn't tell anything about the fraction of users citing similar reasons to purchase.
B is stronger.

Kindly shed some light. Thanks

Thinking about A, that does not make sense. If it were true that it was unlikely - what implications would that have for the conclusion? None really. We need something that relates to the conclusion.

Moving on to B, which is quite tricky! It touches upon both cashemere and angora, and say that they are similar. Thoug, if this were tru, what would that mean? Nothing really. It does not indicate anything about the willingness to purchase.

C does nothing but weakens the argument if true.

D is what we are looking for. Lets say that the reasons are the structure mentioned before. If this was true - than it is more likely that they will buy angora.

E is irrelevant

This is a very loose ended question for supporting a claim. Although D is the correct answer, which I got correct through the process of elimination. All the options need some amount of assumption, with D being the least in that bracket.

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