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Question
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Choices
Curve Question
Difficulty
Psg/Game/S
Difficulty
Explanation
PT16 S3 Q12
+LR
Necessary assumption +NA
A
82%
168
B
10%
164
C
3%
160
D
4%
155
E
1%
159
130
144
159
+Medium 147.952 +SubsectionMedium
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This is a necessary assumption question. We see this because the argument in the stimulus depends on the assumption expressed by the correct answer choice. The assumption must be true for the argument to hold. And if the answer is not true, the conclusion will not be able to follow.

This sounds like a cool technology. The scanner can recognize patterns. Makes sense. See it once; store the data; see it again; match the new scan to the former. Simple enough. No two eyes are the same, hence its reliability because it can’t be confused by any possibility of seeing the same pattern in different eyes. The conclusion in the final sentence may initially seem reasonable enough. Isn’t this exactly what these scanners do? If you don’t see a gap here, that’s okay.

Our approach for NA questions is to keep an open mind going into the answer choices. This is particularly effective in situations like this where we may not see a gap. There is potentially a few things we might anticipate here, but we do not want to enter the AC’s searching for anything in particular. Let’s consider the Answers and let them speak to us. The correct answer choice will suggest the solution. If we’re open to it, we only need to be able to utilize the prompt to follow through and recognize the solution.

Correct Answer Choice (A) This is the right answer. To use negation: If the blood vessels could change to such an extent that the scanner can no longer match the pattern of the current scan to the previous one, then a retina scanner cannot necessarily “be used successfully to determine for any person whether it has ever scanned a retina of that person before.” If I get the right kind of eye disease, they won’t recognize me and I’m back off the grid. This would create a subset of exceptions which would not fit. Because the conclusion is universal, there are no exceptions allowed. This answer tells us that such an exception can not occur, which is necessary for the conclusion to follow.

Answer Choice (B) This is tempting because we understand that most people have two eyes and we recognize a distinction between recognizing eyes and recognizing people. If this led you astray, check the stimulus again. We’re only concluding that the retina scanner can be used to tell if it has scanned a retina of a person before. We don’t limit its methodology in how it might determine this: It could simply scan both eyes, no problem.

An even simpler reason to eliminate this answer choice, however, is that the stimulus has already told us, “no two eyes have identical patterns.” So actually, we already know that every person has different patterns of blood vessels in each eye. Those are two eyes, after all, and “no two eyes have identical patterns.” So not only is this not necessary, it contradicts the stimulus.

Answer Choice (C) We don’t care. Our conclusion is not indicating we can create a global database of scans so that we can ID anyone in the world. It only needs to be able to recognize someone it’s already scanned before. If someone isn’t already in the system, it doesn’t need to be able to recognize them per our conclusion.

Answer Choice (D) What if they’re not? Then some people would not only have different patterns of vessels but also different numbers of vessels. Would that mean the scanners couldn’t recognize people? If anything, that would give them more variation to go on. So if this isn’t true, it may even be helpful. If the negated form of this answer strengthens the argument, then this does not have to be true.

Answer Choice (E) I don’t know how this matters at all. What if there is? How does that bear on whether or not a scanner could recognize you with a second look? If you’ve been scanned by two scanners, then two scanners should be able to recognize you. No big deal. So this is not necessary.