PrepTest 152, Section 2, Question 23
A scientific study provides evidence that crows are(52 more words not shown)
The argument depends on the(2 more words not shown)
- Asome of the(19 more words not shown)
- Bcrows that perceive(10 more words not shown)
- Cmost birds of(18 more words not shown)
- Deven in places(17 more words not shown)
- Ecrows can distinguish(19 more words not shown)
Reading the argument
Recognizing danger and passing that warning to another crow are two different claims. I can imagine a crow's alarm alerting the other birds, but what evidence shows that this happened?
The crows react to people wearing masks years after the trapping. What if all the birds reacting are the same birds that were trapped? Their own memories could explain the response without any warning being passed along.
What we’re looking for
I'd also want to know whether crows just react this way to people in general. If they shriek and dive at any nearby person, the masks and the earlier trapping might have nothing to do with it. For a required assumption, my first guess would address that problem: the observed response needs to mean something about recognizing a threat, rather than being an ordinary reaction to anyone who walks past.
Working the answers
- ACorrect
This addresses the other gap we noticed: communication between crows. If every attacking crow had personally been trapped, the result could reflect only those birds remembering their own experience. Some birds that weren't trapped must participate for this observation to provide the claimed evidence of concerns being passed to other crows. That doesn't prove communication all by itself, but it supplies something the argument needs for the second part of its conclusion.
- B
The crows don't have to respond this way every time they perceive a threat. Sometimes they might fly away instead. The argument uses this observed response as evidence that these birds recognize a threat; it doesn't require shrieking and dive-bombing to be their only possible response to one.
- C
We don't need a claim about most birds of every species. The conclusion is about crows communicating concerns to other crows. Whether a different kind of bird also interprets the crows' behavior as a warning goes beyond what this argument needs.
- D
This gives a reason to doubt the learned-warning story. If crows commonly attack people in these masks even where they haven't been captured, the response may not require the trapping experience or warnings passed along from it. D isn't an assumption the argument depends on.
- E
The first part sounds relevant to my initial concern: can the birds tell the masked people apart from people without masks? But then E adds that crows cannot recognize individual human faces. The experiment doesn't require that limitation. Crows could recognize individual faces as well as masks. We need the whole answer to be required, not just a promising first half.
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