PrepTest 156, Section 2, Question 19
Geologist: As a spinning object's radius decreases, its(71 more words not shown)
Which one of the following,(19 more words not shown)
- AIn the beginning(21 more words not shown)
- BDuring the past(17 more words not shown)
- COnly skillful figure(13 more words not shown)
- DSince the time(13 more words not shown)
- EIncreased volcanic activity(16 more words not shown)
Reading the argument
Is the Earth actually getting smaller overall? That's what I'd want to check before accepting this explanation of its faster rotation.
The geologist gives a chain: more earthquakes move plates inward, that decreases Earth's radius, and a smaller radius makes a spinning object rotate faster. The figure skater pulling in their arms illustrates the last step. We can follow that explanation without importing our own physics knowledge.
What we’re looking for
For a weakener, I'd look at the proposed cause of the faster rotation. Perhaps some other process explains the change. Or perhaps the earthquake movements don't produce the overall decrease in radius the geologist is relying on. An immediate inward movement isn't necessarily the whole story of what happens over a decade.
Working the answers
- A
This describes another period in which increased earthquake activity accompanied a smaller radius. That fits the kind of relationship the geologist proposes; it doesn't undermine it. It also concerns the beginning of the twentieth century rather than the decade the explanation is about.
- BCorrect
Other geological events push against the earthquake-related movements. That means we can't look only at plates moving inward immediately after earthquakes and assume that this gives us the net change in Earth's radius over the decade.
Imagine counting everything added to an account while ignoring withdrawals. The additions don't tell you how much the balance grew. Similarly, movements that counteract the inward shifts weaken the offered explanation for an overall shrinkage and resulting increase in rotation. B needn't establish an exactly unchanged radius to challenge that explanation.
- C
The figure skater is an illustration of the relationship the passage gives us. A detail about which skaters perform the maneuver successfully doesn't establish that the Earth's radius or rotation behaves differently from the stated rule. Our question concerns the explanation for Earth's change, not the skaters' skill.
- D
Knowing that rotation has fluctuated for a long time doesn't explain or challenge the cause of this particular recent increase. The geologist could be right about the last decade even if earlier changes had different causes. General historical variation isn't a competing explanation by itself.
- E
More plate movement doesn't tell us which direction the plates moved or whether the movements offset the inward shifts. The geologist already relies on increased geological activity, so this additional activity could fit that account. Unlike B, E doesn't identify a process counteracting the proposed cause.
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