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The goblin fern, which requires a thick layer of leaf litter on the fo

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The goblin fern, which requires a thick layer of leaf litter on the fo  [#permalink]

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New post 02 Sep 2017, 09:41
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Question Stats:

51% (02:34) correct 49% (02:34) wrong based on 333 sessions

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The goblin fern, which requires a thick layer of leaf litter on the forest floor, is disappearing from North American forests. In spots where it has recently vanished, the leaf litter is unusually thin and, unlike those places where this fern still thrives, is teeming with the European earthworm Lumbricus rubellus, which eats leaf litter. L. rubellus is thus probably responsible for the fern's disappearance.

Which one of the following is an assumption on which the argument depends?

(A) Wherever there is a thick layer of leaf litter in North American forests, goblin ferns can be found.
(B) None of the eartbworms that are native to North America eat leaf litter.
(C) Dead leaves from goblin ferns make up the greater part of the layer of leaf litter on the forest floors where the goblin fem has recently vanished.
(D) There are no spots in the forests of North America where both goblin ferns and earthworms of the species L. rubellus can be found.
(E) L. rubellus does not favor habitats where the leaf litter layer is considerably thinner than what is required by goblin ferns.

Source: LSAT

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Re: The goblin fern, which requires a thick layer of leaf litter on the fo  [#permalink]

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New post 02 Sep 2017, 12:38
The goblin fern, which requires a thick layer of leaf litter on the forest floor, is disappearing from North American forests. In spots where it has recently vanished, the leaf litter is unusually thin and, unlike those places where this fern still thrives, is teeming with the European earthworm Lumbricus rubellus, which eats leaf litter. L. rubellus is thus probably responsible for the fern's disappearance.

Which one of the following is an assumption on which the argument depends?

(A) Wherever there is a thick layer of leaf litter in North American forests, goblin ferns can be found. -We already know this information from the passage. It can't be an assumption.
(B) None of the eartbworms that are native to North America eat leaf litter. -We are worried about the L. Rubellus earthworms. Out of scope.
(C) Dead leaves from goblin ferns make up the greater part of the layer of leaf litter on the forest floors where the goblin fem has recently vanished. -We are not worried about what constitute the various parts of leaf litter.
(D) There are no spots in the forests of North America where both goblin ferns and earthworms of the species L. rubellus can be found. -This will be a weakener.
(E) L. rubellus does not favor habitats where the leaf litter layer is considerably thinner than what is required by goblin ferns. -Correct. The L. Rubellus are found in thick covers of leaf litter that are essential for the growth of goblin fern.
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Re: The goblin fern, which requires a thick layer of leaf litter on the fo  [#permalink]

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New post 02 Sep 2017, 12:48
OA -> E
Opposite is not true i.e L rubellus is not there because leaf layer is already thin.
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Re: The goblin fern, which requires a thick layer of leaf litter on the fo  [#permalink]

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New post 02 Sep 2017, 12:59
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shalabhg27 wrote:
OA -> E
Opposite is not true i.e L rubellus is not there because leaf layer is already thin.


Hi,

(E) L. rubellus does not favor habitats where the leaf litter layer is considerably thinner than what is required by goblin ferns.
Negation: "L. rubellus does not favor habitats where the leaf litter layer is NOT considerably thinner than what is required by goblin ferns".

This means that wherever the litter is thick (not considerably thin), they are not present. --> If they are not present in the thick layer of litter, then this weakens the argument, since it would mean that the thick layer of litter is being thinned out by some other being/natural force than the L. Rubellus.

OA is correct.
Hope that helps !!

P.S.: 1 piece of advice for you; instead of arguing that why the OA is incorrect, try to understand where did you go wrong. Since, this is an official LSAT question, it can't be wrong. It will help you to gain more knowledge.
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Re: The goblin fern, which requires a thick layer of leaf litter on the fo  [#permalink]

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New post 15 Sep 2017, 00:27
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The trigger "˜thus’ helps us locate the conclusion here: L. rubellus is probably responsible for the fern’s disappearance. This is a causation conclusion: L is causing the fern to disappear. What is this conclusion based on? areas where fern recently vanished are teeming with L and have unusually thin leaf litter (and we’re told L eats leaf litter). It certainly seems reasonable to conclude that this is all L’s fault, but we know we must be very careful when making a causation conclusion. The premises offer us a correlation, but that’s never enough to prove causation. Perhaps an unknown factor is causing the fern to vanish, and L didn’t enter those areas until later? This could all just be one big misunderstanding! Let’s diagram the core:

Spots where fern recently vanished have unusually thin leaf litter, which is required by the fern + those spots are teeming with L, which eats leaf litter --> L is probably responsible for the fern’s disappearance

We’re looking for an answer choice that will make a coincidence less likely, and we’ll get rid of answer choices if negating them doesn’t kill the conclusion:

(A) doesn’t mention L so probably wrong; let’s negate it and see what happens: some North American forests with thick leaf litter don’t have any fern. No one ever said fern has to be in every spot that has thick leaf litter! So, even if the opposite of (A) is true, L could still be the reason for the fern’s disappearance. Get rid of this one.

(B) Let’s negate this one too: some earthworms other than L eat leaf litter. Even so, L could still be responsible for the fern’s disappearance. Get rid of this one.

(C) You’d probably expect to find evidence of dead fern in areas where the fern recently vanished. What if the fern’s dead leaves only made up the smaller part of the leaf litter (again, negation)? This changes nothing... L could still be responsible for the fern’s disappearance. Get rid of this one.

(D) Try negation again: what if you could find some spots in North American forests that have both L and fern? Even then, L could still be responsible for the fern’s disappearance _ perhaps the fern will disappear from those spots as well in the near future. Get rid of this one.

(E) Negation has worked really well for us in the first four answer choices, and at this point we’re hoping (E) is right, otherwise we’re in trouble. Let’s try negating this one as well: L favors habitats where the leaf litter layer is considerably thinner than what is required by the fern. Aha! This means that the fern vanished before L arrived! L couldn’t be responsible for the fern’s disappearance!

So (E) is correct.

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Re: The goblin fern, which requires a thick layer of leaf litter on the fo  [#permalink]

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New post 28 Jan 2019, 02:41
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Re: The goblin fern, which requires a thick layer of leaf litter on the fo   [#permalink] 28 Jan 2019, 02:41
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