PrepTest 150, Section 3, Question 17
Since mosquito larvae are aquatic, outbreaks of mosquito-borne(38 more words not shown)
Which one of the following,(11 more words not shown)
- AThe use of(7 more words not shown)
- BHuman populations tend(8 more words not shown)
- CWetland habitats contain(8 more words not shown)
- DWetland habitats host(13 more words not shown)
- EPeriods of drought(13 more words not shown)
Reading the argument
If mosquito larvae need water, more disease after wet weather makes sense. My first thought about wetlands is that they're wet already: perhaps extra rain doesn't change much there.
What we’re looking for
But that doesn't explain why disease gets worse after drought. To resolve this discrepancy, we need something about drier conditions that helps mosquitoes in these particular habitats, despite their need for water. I don't yet know what that would be.
Working the answers
- A
An insecticide ban might help explain why mosquitoes persist in wetlands. It doesn't explain why outbreaks become worse after drought. The ban could apply during wet and dry periods alike; we still need the difference between those conditions.
- B
Sparse human populations don't explain the change after drought. Even if population density affected the number of cases, B gives us no reason for that factor to produce worse outbreaks specifically following dry weather.
- CCorrect
The water supports something besides mosquitoes: insects that eat mosquito larvae. Drought could reduce those predators, allowing more larvae to survive. That gives us a way for drier conditions to benefit mosquitoes indirectly.
My hesitation is that the larvae need water too. Wouldn't drought hurt them as well? It could. The explanation works if the benefit from reduced predation outweighs the loss of breeding habitat; drought needn't mean every bit of water disappears. C doesn't prove that this happens or say that all the predators die. It supplies a relevant relationship that could explain the otherwise surprising result.
Compare E: we'd still have to invent a connection between new plants and mosquito-borne disease. C already supplies the crucial connection between the affected aquatic insects and mosquito survival. That makes it the better explanation.
- D
A wider variety of mosquito species might distinguish wetlands from other habitats. But the variety alone doesn't explain why disease increases after drought. We aren't told that those species respond to dry weather in some way that produces the observed change.
- E
This at least tells us something that drought changes: new plant growth. But what does that growth do to mosquitoes or the diseases they carry? We aren't told. New plants could matter, but we would need an additional relationship to make them explain the outbreak. C gives us an actual feeding relationship with mosquito larvae.
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