PrepTest 107, Section 3, Question 8
The local agricultural official gave the fruit growers(89 more words not shown)
Each of the following, if(6 more words not shown)
- AThe amount of(35 more words not shown)
- BDuring the past(27 more words not shown)
- COver the past(39 more words not shown)
- DSome of the(30 more words not shown)
- EThe effects of(27 more words not shown)
Reading the argument
The proportion of pears lost to insects fell. That's good news for the growers, but what caused the change?
They switched pesticides, so the new pesticide is an obvious possibility. It isn't the only possibility. What if the weather changed during those three years? Perhaps it became too cold for many of the insects, or conditions caused them to move away. The growers could lose a smaller share of their pears even if the new pesticide were no better than the old one.
The official gives the new pesticide credit because the improvement followed the switch. To challenge that inference, I'd look for another change that could explain the reduction in insect damage. My first thought is weather, but any supported alternative explanation could make the pesticide comparison less convincing.
What we’re looking for
This is an EXCEPT question. Four choices will weaken that comparison, and we're selecting the one that doesn't. Keep asking whether each fact helps explain the lower proportion of pears lost without crediting the new pesticide.
Working the answers
- ACorrect
Fewer mature trees may mean the orchards can produce fewer pears. But the reported improvement concerns the proportion of pears lost to insects, not the total number grown or lost.
Imagine an orchard producing 1,000 pears and losing 100, then producing 500 and losing 50. Production and losses both fell, but insects still took 10 percent. A decline in the number of trees doesn't by itself explain why the percentage lost would fall. A changes the potential amount of fruit without providing the alternative explanation we need to weaken the official's argument.
- B
The growers introduced other insect-control programs, and some worked. Those programs could account for at least part of the reduction in damage attributed to the new pesticide. The official hasn't separated the pesticide's effect from the effects of those other efforts. That weakens the comparison, so we eliminate B.
- C
These birds eat the insects that eat the pears. If the birds now spend more of the year in the region, they could reduce the insect population and the damage it causes. That supplies another possible explanation for the lower losses: more time for the birds to eat the pests.
- D
These insects need water to reproduce, and their breeding areas have been shrinking. Fewer insects may be born as a result, leaving fewer to attack the pears. The new pesticide need not receive credit for an improvement caused by reduced breeding habitat.
- E
The old pesticide can continue working after the growers stop applying it, and its effects accumulate. That complicates the before-and-after comparison. Some of the protection during the new pesticide's three years may come from the lingering, accumulated effects of the old one.
We therefore cannot cleanly attribute the improved result to the new product being more effective. E need not establish that the old pesticide explains all of the improvement; it provides a reason to doubt the official's attribution.
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