Self-study
A recent study concludes that prehistoric birds, unlike modern birds, were cold-blooded. ████ ██████████ █ ██████ ████ ████ ████ ██████ █████ █████████ ████ ████████████ ██████ ███ ██████████ ██ █████ ██ ███ █████████ ██ ██████ █████ ██ ███████████ ██████ ██████ ███████████ █████ ███ ███████ ██ ██ █████ ████ ██ ████████████ ████████ ███████ ██████ ████████ ████████ ████ █████ ██ █████████ ████ ███████████ █████ ███ █████ █████ ███████ ██ █████ ██████ █████ ████████ ████ ████ ████ ██████ █████████ ███ █████████ ███ ██ ██ █████████████
"Surprising" Phenomenon
Prehistoric birds had growth rings suggesting they were cold-blooded animals, but dense blood vessels suggesting they were warm-blooded animals.
Objective
A hypothesis resolving this dispute must state a key similarity or difference between prehistoric birds and either cold-blooded or warm-blooded animals. It must allow for prehistoric birds to have both growth rings and dense blood vessels while being exclusively either cold-blooded or warm-blooded.
13.
Which one of the following, ██ █████ █████ ████ ████ ██ ███████ ███ ███████ █████████ █████ ██ █████ ██ ███ █████ ██ ███
a
Some modern warm-blooded ███████ █████ ████ █████ ████ ████ █████ ██ ████ █████████ ████ ████████████ ████████
This does not favor either possibility. Though other warm-blooded species descended from cold-blooded species, it is possible warm-blooded birds descended from warm-blooded prehistoric birds.
b
Having growth rings ██ ███ ███ ████ ████████ █████ ██ ████████████ ████████
This is irrelevant information that does not favor either possibility. It is not stated whether prehistoric birds possessed any other traits of cold-blooded species.
c
Modern birds did ███ ██████ ████ ███████████ ███████ ██ ██████
In dispute is whether prehistoric birds were warm-blooded or cold-blooded, regardless of whether they were ancestors of modern birds. Both studies draw conclusions about prehistoric birds explicitly, so this does not favor either possibility.
d
Dense blood vessels ███ ███ █████ ██ ███ ████████████ ████████
This gets the desired relationship backward. It states that some warm-blooded species do not have dense blood vessels, but admits the possibility that all species with dense blood vessels are warm-blooded.
e
In some cold-blooded ███████ ███ ████ ████ ██ ███████████ ███ ██████ █████ ██ ████ ███████████ ███ █████ █████ ████████
This suggests prehistoric birds were cold-blooded. It implies that dense blood vessels are not necessarily evidence of warm-bloodedness, especially among animals with growth rings, calling into question the conclusion of the second study.