PrepTest 109, Section 3, Question 18
Studies have shown that photosynthesis, the process by(61 more words not shown)
The flawed reasoning in the(13 more words not shown)
- ABecause a high(42 more words not shown)
- BBecause exercise has(25 more words not shown)
- CConsistently consuming more(28 more words not shown)
- DIt has been(35 more words not shown)
- EExcessive use of(27 more words not shown)
Reading the argument
One benefit doesn't erase every possible downside.
Let's accept the stated effect on photosynthesis. More carbon dioxide helps that process, and the industrial activities add carbon dioxide. That gives the author a benefit to discuss. It doesn't establish that everything those activities do is good for agriculture or for the people depending on it.
What about their other effects? Perhaps a change in temperature or pollution reaching the soil could offset the benefit. Those are possible concerns, not facts we need to prove here. The word “purely” is the problem: the author goes from identifying an advantage to ruling out any disadvantage.
To picture the same mistake, suppose a sweet coffee drink makes me more alert. Does that mean the drink has no downside? What if it also keeps me awake when I want to sleep? Accepting the alertness benefit doesn't force us to accept the no-downside conclusion.
What we’re looking for
For the parallel flaw, look for that move: an activity has a benefit, therefore it brings no harm. We need more than an answer that makes a questionable recommendation; we need the same unsupported claim about the whole set of effects.
Working the answers
- A
This argues that if a higher-fiber diet is better than a lower-fiber one, replacing every low-fiber food must be better still. That extends a comparison into total replacement. It isn't the same as pointing to a benefit and declaring the activity completely free of harm.
A isn't automatically sound: a benefit from having more of something doesn't necessarily establish that eliminating every alternative is best. But the form of that mistake differs from the original's “purely beneficial” claim.
- BCorrect
Exercise prevents certain problems, so the author concludes that it causes no harm and a lot of good. The preventive benefits match the photosynthesis benefit. The claim of no harm matches “purely beneficial.”
What about an injury from exercising, or another cost the listed benefits don't address? We can accept that exercise prevents some problems without concluding that it creates none.
B lists several benefits, while the original focuses on one. That difference doesn't change the mistake. One benefit or several benefits still won't establish that there are no drawbacks at all.
- C
This starts with a harmful result of consuming more calories than one expends and recommends periodic fasting to avoid it. We would need to examine why that particular response is required rather than some other way of changing the imbalance. But that isn't the original move from a beneficial effect to a claim of no harmful effects.
- D
The vitamin-and-mineral advantage is used to recommend completely replacing one type of food with another. That could overlook other considerations, such as cost, so it is tempting. But D doesn't conclude that fresh produce can cause no harm. B much more precisely repeats the original's leap from specified benefits to an absence of any downside.
- E
This moves from a problem with excessive use to a recommendation to avoid use. It doesn't begin with a benefit and conclude that there is no harm. The worry is whether a drawback from overuse justifies rejecting use altogether, a different inference from the one we need to match.
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