Self-study
Birds need so much food energy to maintain their body temperatures that some of them spend most of their time eating. ███ █ ██████████ ██ █ ████ ██ █ ███████████ ███████ ██ █ ████ ██ █ █████████████ ███████ ████ ███ ███ ████ ███████ ██████ ███████████ █████ ██████ ████ ████ ███ ███████████ ████ ██████ ████ ████ ██████ ████ ████ ███ █████████████ █████ █████ █ █████ ██████ ██ ██████ ████████ ████ ██████ ████ ████ ███ ████ ██████ ██ ██████
Summary
The author concludes that, between a seed-eating bird and a nectar-eating bird with the same overall energy requirements, the seed-eating bird spends more time eating than does a nectar-eating bird.
Why? Because a given amount of nectar provides more energy than does the same amount of seeds.
Notable Assumptions
The author assumes that eating a given amount of nectar does not take significantly longer than eating the same amount of seeds.
19.
The argument relies on which ███ ██ ███ █████████ ████████████ ████████████
a
Birds of different ███████ ██ ███ █████████ ████ ███ ████ ███████ ██████ ████████████ ██ ████ ██████
Not necessary, because the argument is confined to a comparison of two bird species with the same overall energy requirements. So whether birds typically have the same energy requirements is irrelevant.
b
The nectar-eating bird ████ ███ █████████ ████ ███ ██████
Not necessary, because even if the nectar-eating bird does sometimes eat seeds, the comparison relates to the overall time spent eating. We don’t have any reason to think that sometimes eating seeds would have a significant impact on the overall eating time of a nectar-eating bird.
c
The time it █████ ███ ███ █████████████ ████ ██ ███ █ █████ ██████ ██ ██████ ██ ███ ██████ ████ ███ ████ ██ █████ ███ ███████████ ████ ██ ███ ███ ████ ██████ ██ ██████
Necessary, because if it were not true — if the time it takes for a nectar-eating bird to eat a given amount of nectar IS longer than the time it takes the seed-eating bird to eat the same amount of seeds — then the seed-eating bird might NOT spend more time eating than does the nectar-eating bird. Although the seed-eating bird has to eat more seeds to get the same amount of energy, the lower time required to eat seeds might offset the extra time spent eating more seeds. The author must assume this isn’t true in order to reach the conclusion.
d
The seed-eating bird ████ ███ ████ █ █████ ████ ███████████ ████ ████ ██ ███ █████████████ █████
Not necessary, because the conclusion concerns a comparison between birds with the same overall energy requirement. So whatever impact body temperature might have on energy requirements is already controlled for.
e
The overall energy ████████████ ██ █ █████ ████ ██ ███ ██████ ██ ███████ ████ ██ ███ ████ ██ ███ █████ ███ █████████████ ███████ ███ ███ ███████ ██ ███ ██████ ██ █████ ██ ██████
Not necessary, because the conclusion concerns a comparison between birds with the same overall energy requirement. So whatever impact other factors may have on energy requirements are already controlled for.