PrepTest 107, Section 3, Question 9
The local agricultural official gave the fruit growers(89 more words not shown)
The official's conclusion is most(22 more words not shown)
- Apeach trees grown(15 more words not shown)
- Bpeach trees grown(16 more words not shown)
- Cpear trees grown(15 more words not shown)
- Dpear trees grown(15 more words not shown)
- Epear trees grown(16 more words not shown)
Reading the argument
The new pesticide was followed by less insect damage, but the timing alone doesn't tell us that it caused the improvement. Maybe colder weather drove insects away during those years. Maybe another local change reduced their numbers. Either way, losses could fall even if switching pesticides made no difference.
This question gives us a way to strengthen the official's conclusion. It asks which group of trees would help most if that group did not show a reduction in fruit losses. So we want a useful comparison: pear trees nearby that kept receiving the old pesticide.
Why that group? They would be growing the same fruit in the same district, but using the other pesticide. If the new-pesticide trees improved and those old-pesticide trees did not, it would be harder to credit a general local improvement that helped all the orchards. The difference in treatment would become a more convincing explanation.
What we’re looking for
Try to keep the relevant conditions alike. Changing the kind of fruit or the location introduces another possible reason for different results. This comparison won't guarantee that every detail of the orchards is identical, but it will give us the clearest test offered here.
Working the answers
- A
These are peach trees, not pear trees. Different fruits may attract different insects or respond differently to the same pesticide. If the new pesticide didn't reduce damage to peaches, that wouldn't give us the comparison between old and new pesticides on pears that we want.
- B
We again have peach trees, and now they receive both pesticides. That changes the fruit and the treatment. A lack of improvement in this group wouldn't isolate the difference between the old and new pesticides on the original pear orchards.
- CCorrect
These are pear trees in the same district, still treated with the old pesticide. If their losses didn't decline while the new-pesticide orchards' losses did, the improvement would be associated with which pesticide the trees received.
That makes a district-wide change, such as weather that generally drove away pear-eating insects, a less satisfying explanation. We have a closer comparison supporting the new pesticide's effectiveness without having to assume that nothing else could possibly differ.
- D
This group is in a different district and receives neither pesticide. A lack of improvement there might reflect different local conditions. And comparing the new treatment with no treatment doesn't directly show that it beats the old treatment. C preserves both the district and the old-pesticide comparison.
- E
This group uses the new pesticide in a neighboring district. If it failed to improve, that might reflect different conditions in that district or a limitation of the new pesticide. It doesn't give us the local old-pesticide group we need to make the original comparison more persuasive.
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