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100 points for $49 worth of Veritas practice GMATs FREE VERITAS PRACTICE GMAT EXAMS Earn 10 Points Per Post Earn 10 Points Per Thanks Earn 10 Points Per Upvote Ivory Billed Woodpecker This topic has expert replies GMAT/MBA Expert GMAT Instructor Posts: 2193 Joined: 22 Feb 2010 Location: Vermont and Boston, MA Thanked: 1186 times Followed by:512 members GMAT Score:770 by David@VeritasPrep » Sun Sep 05, 2010 5:49 am Choice B is designed to be a specific type of distraction, let me explain and you can tell me what you think. The way that I would describe the reason that B is not correct is this: B indicates that possible evidence for the presence of the ivory-billed is not there (i.e. the peculiar sound of the tapping). Yet it is not stated that this sound will always be heard. So this is what I would call sufficient evidence, but not necessary evidence. If you have the sound, then you likely have the woodpecker (it is sufficient). But the absence of the sound, does not mean the absence of the woodpecker (not neccessary). On the other hand, choice D is directly weakens the only evidence that they have for the ivory-billed, the large white wing patches. It is true that since the patches are present for both types of birds it is still possible that this is the ivory-billed, but since that bird has not been seen for decades it is very damaging to have the only evidence in favor of the bird being an ivory-billed turn on not to be a true indication of that bird. (As to the video versus observations, I think that seeing the wing patches on the video can be considered an "observation.") Veritas Prep | GMAT Instructor Veritas Prep Reviews Save$100 off any live Veritas Prep GMAT Course

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by samarpan_bschool » Sun Sep 05, 2010 6:36 am
B indicates that possible evidence for the presence of the ivory-billed is not there (i.e. the peculiar sound of the tapping). Yet it is not stated that this sound will always be heard. So this is what I would call sufficient evidence, but not necessary evidence. If you have the sound, then you likely have the woodpecker (it is sufficient). But the absence of the sound, does not mean the absence of the woodpecker (not neccessary).
I missed this point - Thanks