PrepTest 156, Section 2, Question 14
When polar ice caps grow (during ice ages,(75 more words not shown)
The information given most strongly(12 more words not shown)
- AAverage global temperatures(16 more words not shown)
- BPolar ice caps(17 more words not shown)
- CThe beginning of(15 more words not shown)
- DThe polar ice(14 more words not shown)
- EAn ice age(13 more words not shown)
Reading the argument
The oxygen is a clue about what the ice was doing. We don't need to know its effects on shellfish to use that clue. As the ice caps grow, lighter oxygen collects in the ice, leaving seawater with a greater concentration of the heavy form. Marine organisms absorb it. When the ice shrinks, the concentration of heavy oxygen in the seawater decreases.
Now put the 30,000 years on a simple timeline. For the first 20,000 years, heavy-oxygen concentrations in shellfish increase. That points to growing ice caps. For the next 10,000 years, the concentrations decrease. That points to shrinking ice caps.
What we’re looking for
The question asks for the hypothesis most strongly supported by that information. I'd stay with that sequence: growth followed by shrinkage. We haven't been given exact global temperatures, starting ice sizes, or the amount of ice gained and lost, so answers about those details would require more information.
Working the answers
- A
This compares the temperature at year 10,000 with the temperature 20,000 years later, at the end of the period. Our timeline doesn't give either temperature. Knowing that the ice was growing during one stretch and shrinking during another doesn't establish that temperatures at those two points were equal.
- B
We don't know whether more ice was lost than gained. Twenty thousand years of growth followed by ten thousand years of melting doesn't settle the amounts: growth might be slow and melting rapid, or the reverse. We therefore can't compare the ice caps' size at the beginning with their size at the end.
- C
Why think the ice age began exactly when our 30,000-year record begins? The ice could have been growing well before then. The record supports continued growth during its first 20,000 years, not the onset or full duration of an ice age.
- DCorrect
This follows the oxygen record directly. Increasing heavy oxygen during the first 20,000 years points to ice-cap growth; decreasing heavy oxygen during the final 10,000 years points to shrinkage. D keeps to the change the evidence actually lets us track.
- E
The first 20,000 years show growing ice caps, not the shrinking that would support this description of an ice age ending. We also don't know how long the broader ice age had already lasted. The supported transition to shrinking comes after those first 20,000 years.
More Must Be True questions
Learn the LSAT our way
Our platform drills Must Be True questions at your level and adjusts as you improve.