PrepTest 118, Section 1, Question 2
Commentator: Many people argue that the release of(72 more words not shown)
Which one of the following,(9 more words not shown)
- AExtraterrestrial influences on(11 more words not shown)
- BNatural events, such(12 more words not shown)
- COur earliest ancestors(17 more words not shown)
- DThe ozone layer(8 more words not shown)
- EScientists have discovered(16 more words not shown)
Reading the argument
A much bigger disruption caused no significant harm before. I can see why that makes the commentator less worried. But were the two situations alike in every way that matters?
At first, I'd ask whether the supernova caused the same amount of damage. The argument answers that: it caused more. So simply objecting that today's damage might be bigger won't work. We need another difference.
What if one powerful burst and a continuing release of chemicals affect us differently?
Maybe a slower, ongoing problem could matter even when an earlier burst did not. That's a possibility to investigate, not a fact we've been given. The size of the disruption may not settle the comparison.
What we’re looking for
For a weakener, I'd look for a reason the chlorofluorocarbons, or CFCs, could harm people despite what happened 300,000 years ago. Something relevant has to separate that earlier event from our situation today.
Working the answers
- A
How often extraterrestrial and terrestrial influences occur doesn't tell us whether this release of CFCs will harm humans. My concern about an ongoing release would need a connection between that pattern and its effects. A gives only the relative frequency of two broad categories of events, leaving that connection unaddressed.
- B
Volcanoes can damage the ozone layer too. But the commentator's conclusion concerns whether CFCs harm humans through ozone damage. Adding another source of ozone damage doesn't tell us why the evidence about our ancestors is a poor basis for that conclusion.
- CCorrect
This finds a different problem with the comparison. I was considering differences between the damaging events; C points to a difference between the people exposed to them.
Our ancestors were more resistant to harmful ultraviolet radiation than we are. Then their getting through a larger disruption without significant effects doesn't show that we can safely handle a smaller one. What was tolerable for them could still hurt us. C challenges the comparison without denying the historical evidence.
- D
Slow recovery could make ozone damage last, but D doesn't distinguish the earlier event from the present one in a way that undermines the argument. The layer could have recovered slowly after the supernova too. We still need to know why the ancestors' experience doesn't support the commentator's reassurance.
- E
What genetic changes? They might have affected height or some other trait unrelated to ultraviolet radiation. The mere fact that changes occurred doesn't tell us that our ancestors were more resistant, less resistant, or harmed by the event. C supplies the relevant difference that E leaves unspecified.
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