Self-study
A scientific study provides evidence that Conclusion crows are capable of recognizing threatening people and can even pass their concerns on to other crows. ███████████ ███████ ██████ ███████ █████ ███████ ████ █████ ███ ████ ████████ ████ ██ ███ ████ █████ █████ ██████ ██████ ███████ ███ ████ █████ ████ █████ ███ █████ ███ ████ ███████ ████ ████████ ██ ███ ███████████ ██ ██████
Summary
The author concludes that crows are able to recognize threatening people and can pass their concerns on to other crows.
What makes the author think this?
Because in a study, researchers wore rubber caveman masks and trapped wild crows. The researchers then released the crows in the same area.
Years later, people wearing the same rubber caveman masks went near the area the crows had been released. Crows shrieked at and dive-bombed the people in the masks.
Notable Assumptions
The author assumes that at least some crows that attacked the people in the masks recognized those people. (This is necessary for the portion of the conclusion referring to “recognizing threatening people.”)
The author also assumes that at least some of the crows that attacked the people in the masks were NOT the same crows that were caught years before. (This is necessary for the portion of the conclusion asserting that crows can “pass their concerns on to other crows.”)
23.
The argument depends on the ██████████ ████
a
some of the █████ ████ ████████ ██ ███ ███████████ ██████ ███████ ███ █████ ████ ███ █████ ███ █████ ████ ███ ████ ███████
Necessary, because if this were not true — if NONE of the crows that attacked the people wearing the masks were not among the crows that had been trapped (in other words, if every one of the crows were part of the crows that had been trapped years before) — then we have no support for the claim that crows “can pass their concerns on to other crows.” If the attacking crows were the same ones that were caught before, that raises the possibility that they did not pass their concerns to other crows — they might have simply remembered the masks that caught them before and reacted to those masks.
b
crows that perceive ██ ██████████ ██ ███████████ ██████ ███████ ██ █████████ ███ ████████████
Not necessary, because even if crows that perceive an individual as threatening do NOT always respond by shrieking and dive-bombing, it can still be the case that any crow that responds by shrieking and dive-bombing perceives an individual as a threat. Another way to put it is that the author assumes “shriek and dive-bomb → perceives as threatening.” (B) reverses this assumption.
c
most birds of ███ ███████ ████ ██████ █ ██████ ██ ███████████ ██ ████ ███ █████ █████████ ██ ███ ████████████ ████ ██████
Not necessary, because the argument concerns only how crows behave and what crows are capable of. What other bird species do has no effect on the reasoning, which is based only on observations of crows.
d
even in places █████ █████ ████ █████ ████ █████████ ████ █████ ████ ██████ ██ ███ █████████ ██████ ███████ ███████ █████
Not necessary, because (D) arguably weakens the argument if assumed. If most crows will attack people wearing caveman masks, even in places where crows have never been captured, that suggests attacking people wearing caveman masks may simply be a common reaction of crows, and not necessarily evidence of “recognizing” people who are threatening.
e
crows can distinguish ███████ ██████ ███ ███ ███████ ███████ █████ ███ █████ ███ ███ ████ ███ ████ ██████ █████████ ██████████ █████ █████
Not necessary, because the study did not involve people showing their unmasked faces. So whether crows can “recognize individual human faces” has no bearing on the reasoning. Even if crows can recognize individual human faces, that doesn’t undermine the argument.