PrepTest 113, Section 3, Question 2
For the last three years, entomologists have been(66 more words not shown)
Which one of the following(8 more words not shown)
- AAll varieties of(7 more words not shown)
- BIf a crop(14 more words not shown)
- CThe chances of(18 more words not shown)
- DNo parasite of(11 more words not shown)
- EIn the last(11 more words not shown)
Reading the argument
They looked for the wrong whitefly. That could be a problem, but does it make three years of searching useless? The goal was to find a parasite that could control the crop pest. Thinking the pest was a sweet-potato whitefly, the researchers searched among parasites of that insect. The genetic result corrects the identification: the pest is a silverleaf whitefly. I can understand why that discovery makes us question the search.
But what if the same parasite attacks both species? A parasite found while studying the sweet-potato whitefly might also help control the silverleaf whitefly. Different names for the insects don't establish entirely different parasites. The original search could still have taken the researchers somewhere useful.
What we’re looking for
The required assumption should block that overlap. The author needs the searched group of parasites to be separate from the group that attacks the actual pest. Otherwise, the mistaken identification alone doesn't justify calling all the effort wasted.
Working the answers
- A
We don't need every variety of sweet-potato whitefly to damage crops. The problem concerns a particular new pest and whether the search directed at another insect could help control it. Some harmless varieties could exist without affecting the author's reasoning. A adds a sweeping claim about the other insect's varieties.
- B
Finding a parasite doesn't have to guarantee a usable control method. Perhaps some parasites are too ineffective or difficult to use. The argument can still claim this particular search was wasted without assuming that every parasite of every crop pest is useful. B is a much broader guarantee than the reasoning needs.
- C
Correct identification might improve the next search, but that doesn't establish whether the past search was wasted. The actual pest could be especially difficult to control, leaving poor prospects even now. The author doesn't need to compare the researchers' old and new chances of success to argue that they searched the wrong group.
- DCorrect
This rules out the crossover we were considering. No parasite of the sweet-potato whitefly is also a parasite of the silverleaf whitefly. The author relies on that separation to treat the search among the first insect's parasites as useless for controlling the second.
Without it, saying 'different species' would leave our objection unanswered: some of the parasites under investigation might attack the real pest too. The assumption closes that specific route by which the old search could still help.
- E
The researchers might have found plenty of parasites of the sweet-potato whitefly. The author's complaint is that those parasites concern the wrong pest, not that the researchers found nothing. Discoveries can exist and still be judged unhelpful for the intended task. E confuses finding parasites with finding useful parasites of the target insect.
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