Self-study
Horses, although descended from a forest-dwelling ancestor, thrive in grasslands. ██ ███ ████ █ ███████ ██████ ██████ ████ ████ ███████ █████ ██████ ██ ██████████ ████████ ████████ ██ █ █████ ███████ ██ ███████████ ███ ████ ██████ █████ ██████ ██████ █████ ███ ██████ █ ████ ██████ ████ ████████ █ ██████ ██ ████████
"Surprising" Phenomenon
The population of horses peaked 25,000 years ago during a cold period, and then rapidly declined during a warming period.
Objective
The correct answer will explain why the horse population peaked and declined in correlation with global temperatures. This explanation will likely show that the cooler period was favorable for horses, while the warming period was in some way difficult for horses. Since the stimulus states that horses thrive in grasslands, the explanation may involve how grasslands respond to warming and cooling.
3.
Which one of the following, ██ █████ ████ █████ ██ ███████ ███ ███ █████ ██████████ ██████ ██████ █████ ███ ███ ████ ███████ █████████
a
The forest-dwelling ancestor ██ ██████ ███ ████ █████ ███████ ████ ███████
We’re talking about grassland-dwelling modern horses, not their forest-dwelling ancestors, so this doesn't help us. This also doesn't tell us whether size impacts horses’ ability to withstand cooling and warming.
b
The only true ████ █████ ████████ ██████ ████████████ ██████ ████████ ███ ████ ██████████ ██ ███████ █████
So at least one kind of horse thrives in cold grasslands. We already know from the stimulus that horses prefer grasslands, and this doesn't explain how temperature changes affect horses' survival.
c
Some modern species ████ ███ ███████ ██ ███████ ████ ██ ███████ ███████ ███ ████ ██████████ ██ ███████
Like in (B), we already know that horses like grasslands. But it doesn't help us to explain why horses peaked during a cool period. It doesn’t matter if some horse relatives thrive in warm climates.
d
During cold periods █████ ███ █████████ ███████████ ███ █████ ████ ██ ██████ ██ ██████ ████ ███ ███████ ██████
Horses thrive in grasslands. Cold periods provide horses with ample habitats, while warmer periods turn grasslands into forests. This explains why horses peaked during a cold period and declined rapidly during a warm one.
e
Several cycles of █ ████ ██████ ████████ ██ █ ██████ ██ ███████ ████ ████████ ██ ███ ████ █ ███████ ██████
We've already established that these cycles occur, and this detail doesn't give us more useful information about the horse population changes 25,000 years ago.