PrepTest 111, Section 4, Question 5
One of the advantages of Bacillus thuringiensis (B.t.)(71 more words not shown)
Which one of the following(7 more words not shown)
- AChemical insecticides cause(12 more words not shown)
- BNo particular B.t.(6 more words not shown)
- CB.t. toxins do(9 more words not shown)
- DInsects build up(10 more words not shown)
- EBirds and rodents(10 more words not shown)
Reading the argument
Killing the pests while leaving their predators alone sounds useful. If an insect eats the pests we're trying to control, we have a reason to want that insect to survive. The passage says a B.t. toxin can often target a pest without harming those predators, and it reports no known harmful effects on mammals or birds.
But what does the treatment cost? Does it damage the crop we're trying to protect? Imagine spraying strawberry plants to save them from insects, only to have the spray kill the plants. The treatment's selectivity toward insects wouldn't make that a good solution.
Those are possibilities to investigate, not facts about B.t. The problem is that being better in one respect doesn't establish being preferable overall. The author has described an advantage without comparing possible disadvantages.
What we’re looking for
We're asked to weaken that recommendation. I'd look for a drawback relevant to using B.t. instead of chemical insecticides in an insect pest management program. High cost or crop damage could work, but another reason the treatment performs poorly could matter too.
Working the answers
- A
This is consistent with the claimed advantage of B.t.'s selectivity. Chemical insecticides harm a wider range of insect species, and that wider range could include insects we want to keep, such as predators of the pests. A doesn't establish a downside of B.t. that offsets the benefit the author describes. Mentioning the chemical alternative is relevant to the comparison, but the fact given doesn't weaken it.
- B
We aren't trying to kill every insect. The stated advantage is precisely that a toxin can kill a pest while sparing other insects. A limited range of activity is therefore compatible with the purpose of the program. B would need to show a failure to control the target pests, not merely a failure to kill all insects.
- C
This is an insect-control treatment, not a weed killer. Weeds could require a separate treatment without making B.t. a worse choice for controlling insects. Criticizing an LSAT class for not improving someone's exercise routine would have the same problem: the criticism concerns a different job from the one being evaluated.
- DCorrect
This gives us a different drawback from the cost and crop-damage possibilities. If insects develop resistance more readily to B.t. toxins, the toxins can lose effectiveness against the very pests they are meant to control sooner than chemical insecticides would.
Sparing helpful insects is an advantage only one part of the comparison captures. We also care whether the treatment continues to work against harmful insects. D gives a comparative disadvantage on that central function, so it weakens the claim that selectivity makes B.t. preferable overall.
- E
Birds and rodents might be bigger problems while insects remain a problem worth treating. The conclusion recommends B.t. as a component of insect pest management, not as a cure for every source of crop damage. E doesn't show that chemical insecticides do the insect-control job better.
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