A
One hypothesis about why fish living near coral reefs exhibit such bright colors is that the fish are camouflaged by their bright colors.
B
The fact that many species use camouflage to avoid predators is one reason to believe that brightly colored fish living near reefs do too.
C
The suggestion that the fish living around coral reefs exhibit bright colors because they are camouflaged by the reefs is mistaken.
D
A reef stripped of its fish is relatively monochromatic.
E
It turns out that the corals in a coral reef are mostly dull hues of brown and green.
A
It helps establish the scientific importance of the argument’s overall conclusion, but is not offered as evidence for that conclusion.
B
It is a hypothesis that is rejected in favor of the hypothesis stated in the argument’s overall conclusion.
C
It provides the basis for an analogy used in support of the argument’s overall conclusion.
D
It is presented to counteract a possible objection to the argument’s overall conclusion.
E
It is the overall conclusion of the argument.
Researcher: Over the course of three decades, we kept records of the average beak size of two populations of the same species of bird, one wild population, the other captive. During this period, the average beak size of the captive birds did not change, while the average beak size of the wild birds decreased significantly.
"Surprising" Phenomenon
Why did the average beak size of wild birds shrink while the average beak size of captive birds stayed constant?
Objective
Any hypothesis explaining these findings must state a difference between the birds in the wild and the birds in captivity that explains why the beaks of the wild birds apparently shrunk. It may be a physical difference between the bird populations or it may be a difference in the way the birds were apprehended and measured.
A
The small-beaked wild birds were easier to capture and measure than the large-beaked wild birds.
This does not explain why the average beak size of wild birds decreased. It would explain why wild birds had smaller beaks than captive birds, but does not state that they became any less difficult to capture over time.
B
The large-beaked wild birds were easier to capture and measure than the small-beaked wild birds.
This does not explain why the average beak size of wild birds decreased. Even if more large-beaked wild birds were captured, it remains a mystery why their average beak size decreased over time.
C
Changes in the wild birds’ food supply during the study period favored the survival of small-beaked birds over large-beaked birds.
This explains why wild birds’ beaks shrunk over the study period. Birds with smaller beaks were favored by natural selection, so they became more prominent in the wild, while captive birds did not experience that change.
D
The average body size of the captive birds remained the same over the study period.
This consistency among captive birds does not explain why the wild birds’ beaks decreased in size. It is possible the average body size of wild birds remained the same as well.
E
The researcher measured the beaks of some of the wild birds on more than one occasion.
This does not explain why the wild birds’ beak measurements decreased. It is not implied that the birds measured repeatedly had beaks that were any larger or smaller than average.