Lyme disease is caused by a bacterium transmitted to humans by deer ticks. Generally, deer ticks pick up the bacterium...
GMAT Critical Reasoning : (CR) Questions
Lyme disease is caused by a bacterium transmitted to humans by deer ticks. Generally, deer ticks pick up the bacterium while in the larval stage by feeding on infected white-footed mice. However, certain other species on which the larvae feed do not harbor the bacterium. If the population of these species increased, more of the larvae would be feeding on uninfected hosts, so the number of ticks acquiring the bacterium would likely decline.
Which of the following, if true, strengthens the argument?
Passage Analysis:
| Text from Passage | Analysis |
| Lyme disease is caused by a bacterium transmitted to humans by deer ticks. |
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| Generally, deer ticks pick up the bacterium while in the larval stage by feeding on infected white-footed mice. |
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| However, certain other species on which the larvae feed do not harbor the bacterium. |
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| If the population of these species increased, more of the larvae would be feeding on uninfected hosts, so the number of ticks acquiring the bacterium would likely decline. |
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Argument Flow:
We start with basic facts about how Lyme disease spreads through ticks, then learn how ticks get infected by feeding on mice. The argument then introduces the key insight that some animals don't carry the bacteria, leading to the conclusion that increasing these clean animals would reduce tick infections.
Main Conclusion:
If we increase the population of animal species that don't carry the Lyme bacteria, fewer ticks will become infected because more tick larvae will feed on these clean hosts instead of infected mice.
Logical Structure:
The argument uses a simple cause-and-effect chain: more clean animals → more larvae feeding on clean hosts → fewer infected ticks. The logic assumes that if larvae have more access to uninfected food sources, they'll naturally encounter fewer infected ones, reducing overall bacterial transmission.
Prethinking:
Question type:
Strengthen - We need to find information that makes the conclusion more believable. The conclusion is that if uninfected animal populations increase, fewer ticks will acquire the bacteria.
Precision of Claims
The argument makes claims about quantities (number of infected ticks declining) and causal relationships (more uninfected hosts leading to fewer infected ticks). The key mechanism is that tick larvae will shift their feeding from infected mice to uninfected animals.
Strategy
To strengthen this argument, we need information that supports the causal chain: more uninfected animals → more larvae feeding on them instead of infected mice → fewer infected ticks. We should look for evidence that confirms this feeding shift will actually happen, that the uninfected animals are actually viable alternatives, or that eliminates potential obstacles to this process.
This tells us that infected ticks aren't harmed by carrying the bacteria, but this doesn't strengthen our argument about reducing infections. We're focused on preventing ticks from getting infected in the first place by having them feed on clean animals. Whether infected ticks are healthy or sick doesn't impact our proposed solution of increasing uninfected animal populations.
This addresses human-mouse transmission, but our argument is specifically about the tick-mouse-human transmission chain. We're trying to reduce tick infections by having fewer larvae feed on infected mice. How humans interact directly with mice is irrelevant to our proposed mechanism of increasing uninfected animal populations to redirect larval feeding.
This directly strengthens our argument because it confirms that each larva gets exactly one feeding opportunity during the critical stage when it can acquire the bacteria. This means the feeding choice is decisive - feed on an infected mouse and become a carrier, or feed on an uninfected animal and remain clean. If larvae fed multiple times, our strategy might fail because they could feed on both clean and infected hosts. This 'one-shot' rule makes our proposed solution much more reliable.
This actually works against our argument rather than strengthening it. If one infected mouse can infect many larvae, then even small numbers of infected mice could still create lots of infected ticks. This suggests that simply increasing uninfected animals might not be as effective as we hoped, since the infected animals are very efficient at spreading bacteria to multiple larvae.
This tells us about other bacterial diseases, but we're specifically concerned with Lyme disease bacteria. Whether these alternative animals carry different bacteria doesn't affect our argument about reducing Lyme disease transmission. We only care whether they carry the Lyme bacteria (which we already know they don't).