Self-paced
By examining fossilized beetles, a research team has produced the most detailed description yet of temperatures in Britain over the past 22,000 years. ███████ ██ ███████ ████ █████ █████ ████ ████████ ███ ██████ ████ ███████████ ██ ███████ ███████ █████ ██ ███ ████ █████ ████ █████ ██ ████ ██ ███ ████ ███████ ███ █████ ███████████ ██████████ ██ ███ ████████ ██████ ███████ ████ ████ ██ █████████ ███ ███████ ██████ ███████████ ████ █████ ████ ███████ ██ ████ █████ ███ ███████
Objective: Identify a Necessary Assumption
Although we're looking for a necessary assumption, the stimulus doesn't really contain an argument. Instead, it tells us some facts about a procedure used by some researchers. The assumption we're looking for will be necessary for that procedure to make sense.
The researcher's procedure was for the purpose of determining temperature ranges over the past 22,000 years. They did this by examining and dating beetle fossils—specifically, fossils of species that still exist. They then matched the beetle species' temperature tolerances to the age of the fossils, to figure out the maximum possible summer temperature of different places and times.
Especially without a real argument to look at, it's difficult to predict a necessary assumption. We can proceed using process of elimination, and relying on our negation or must-be-true tests to confirm when an answer choice is incorrect.
25.
The procedure of the researchers ███████ █████ ███ ██ ███ ██████████
a
Beetles can tolerate ████ ███████ ██████ ████ ████ ████████
Let's negate (A): beetles can tolerate cold weather equally well or better than warm weather. But even if beetles' warm weather tolerance is relatively low, it still makes sense that beetles would live somewhere no warmer than what they can tolerate. The procedure is still reasonable.
b
Fossils of different ███████ █████ ██ ███ ████ █████ ████████ ██ █████████ ████████
Let's negate (B): fossils of different species in the same place sometimes belonged to the same period. If anything, negating (B) would allow the researchers to get more accurate results, because they would have more overlapping data to work with. It certainly doesn't undermine the procedure.
c
The process of ██████ ██ ████ ████████ ███ ███████ ████ ███ █████ ██████████
Let's negate (C): the process of dating beetles is equally or less reliable than for other organisms. But since we don't know the reliability of dating other organisms, this doesn't tell us much. It's not necessary to compare beetle dating favorably to a reference point we don't actually have.
If (C) said that the process of dating beetles was reasonably accurate, then it could be necessary.
d
The highest actual ██████ ███████████ ██ █ █████ ███ ██████ ███████ ███ ███████ ██ ███ ███████ ████████████ ████ █████ ████ ████ █████████ ██ ████ ██ ███ ██████ ███████ █████ █████ ███ █████ ██ ████ ███████
Let's negate (D): the highest actual summer temperature was different from the average of each beetle species' tolerance. But this doesn't harm the procedure because the stimulus isn't about actual temperature; it's just about the highest possible temperature. So (D) isn't necessary.
Digging further into (D), it just doesn't make sense given the stimulus. It's reasonably to infer that the maximum possible temperature would be no higher than the lowest beetle tolerance, right? If it were any higher, that beetle wouldn't be present. But averaging across beetles would have exactly that effect. So not only is (D) unnecessary, it's not compatible with the facts.
e
The temperature tolerances ██ ███ ██████ ███████ ███ ███ ██████ █████████████ ██████ ███ ███████████ ███████
Let's negate (E): beetle species' temperature tolerances changed significantly during the 22,000-year period. That suddenly makes the researchers' procedure look a whole lot less reliable. The whole idea of using still-existing species is to apply their current, known temperature tolerances to the past. If their tolerances have changed, we can't reliably do that, which undermines the procedure.