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#19 -The goblin fern, which requires a thick layer of leaf

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I dont understand why D is wrong and E is correct??
Dave Killoran
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Hi Akansha,

Thanks for the question! In simple terms, in this Assumption question (D) is way too strong to be correct, whereas (E) is related to the causal nature of the conclusion. Let's look at each:

    Answer choice (D): Does the author assume that there are absolutely no spots at all where the ferns (thriving or not) and earthworms are found together? No, that's simply far beyond anything the author suggested or needs to have for the argument to make sense. If we negate this answer, we arrive at: "There are no spots in the forests of North America where both goblin ferns and earthworms of the species L. rubellus can be found." How does the author respond to that, or does it kill the argument? It definitely doesn't kill the argument, and the author would likely respond along the lines of, "Yes, they are found together, and in those areas eventually the earthworm will eat the leaf litter the fern needs, leading to its disappearance."

    Answer choice (E): The causal belief in this problem is that the earthworm is eating the thick layer of leaf litter the fern loves, which ultimately leads to the disappearance of the fern. It's a causal chain: earthworm :arrow: reduced leaf litter :arrow: disappearing fern. Inside that chain there has to be a belief that the earthworm actually inhabits those areas of thick leaf litter. But, what if the earthworm didn't like the places where the leaf litter was as thick as what the fern likes? That might very mean that the earthworm is hanging out in places with less leaf litter, which are also the kind of places that the ferns never thrived to begin with. If that's the case, maybe the earthworm isn't what's causing the problem. That would hurt the argument, and that's exactly what the negation of this answer does.

Please let me know if that helps. Thanks!
Dave Killoran
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