Self-study
The size of the spleen is a good indicator of how healthy a bird is: sickly birds generally have significantly smaller spleens than healthy birds. ███████████ █████ █████ ██ ████████ █████ ████ ███ ████ ██████ ██ █████████ ███ █████████████ ███████ ███████ ████ █████ ██████ █████████████
Summary
The size of a bird’s spleen is a good indicator of the bird’s health. Sick birds usually have much smaller spleens than healthy birds. Researchers found that birds killed by predators generally had much smaller spleens than those killed accidentally.
Strongly Supported Conclusions
Healthier birds are less likely to be killed by predators and sickly birds are more likely to be killed by predators.
Predators may target weaker birds over healthier birds.
Accidental deaths in birds may be less related to healthiness than death by predation.
4.
Which one of the following ██ ████ ████████ █████████ ██ ███ ███████████ ██████
a
Predators are unable ██ ████ ███████ ██████
Unsupported. We know that birds killed by predators generally have smaller spleens, but we cannot conclude that predators are unable to kill healthy birds.
b
Most birds with ███████ ████ ███████ ███████ ███ ██████ ██ ██████████
Unsupported. Birds killed by predators generally have smaller spleens, but we cannot conclude that most birds with small spleens are killed by predators. Perhaps most birds die from some other cause but, of the few birds killed by predators, many have small spleens.
c
Predators can sense ███████ █ ████ ██ █████
Unsupported. Predators tend to kill birds with smaller spleens, but this does not mean that predators can sense whether a bird is sick. Perhaps sick birds are simply slower than healthy ones and cannot escape predators. The stimulus doesn’t give us enough information on this.
d
Sickly birds are ████ ██████ ████ ███████ █████ ██ ██ ██████ ██ ██████████
Strongly supported. Sickly birds usually have smaller spleens than healthy birds. And birds with smaller spleens are more likely to be killed by predators. So, sickly birds are more likely than healthy birds to be killed by predators.
e
Small spleen size ██ ███ ██ ███ ████ ██████ ██ ████████ ██ ██████
Unsupported. Sick birds tend to have small spleens, but we cannot conclude that small spleens cause sickness in birds.