Although exposure to asbestos is the primary cause of mesothelioma, a slow-developing cancer, researches believe that infection by the SV40...
GMAT Critical Reasoning : (CR) Questions
Although exposure to asbestos is the primary cause of mesothelioma, a slow-developing cancer, researches believe that infection by the SV40 virus is a contributing cause, since in the United States 60 percent of tissue samples from mesotheliomas, but none from healthy tissue, contain SV40. SV40 is a monkey virus; however, in 1960 some polio vaccine was contaminated with the virus. Reseachers hypothesize that this vaccine was the source of the virus found in mesotheliomas decades later.
Which of the following, if true, most strongly supports the researchers' hypothesis?
Passage Analysis:
| Text from Passage | Analysis |
| Although exposure to asbestos is the primary cause of mesothelioma, a slow-developing cancer, researches believe that infection by the SV40 virus is a contributing cause |
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| since in the United States 60 percent of tissue samples from mesotheliomas, but none from healthy tissue, contain SV40 |
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| SV40 is a monkey virus; however, in 1960 some polio vaccine was contaminated with the virus |
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| Researchers hypothesize that this vaccine was the source of the virus found in mesotheliomas decades later |
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Argument Flow:
The passage starts by establishing that SV40 virus contributes to mesothelioma, then provides statistical evidence showing SV40 is present in cancer samples but not healthy ones. It then explains how humans could have been exposed to this monkey virus through contaminated vaccines in 1960, leading to the hypothesis that this vaccine contamination explains today's cancer cases.
Main Conclusion:
The contaminated polio vaccine from 1960 was the source of SV40 virus found in mesothelioma cases decades later.
Logical Structure:
The argument uses correlation evidence (SV40 present in 60% of cancer samples vs 0% in healthy samples) combined with historical facts about vaccine contamination to support a causal hypothesis linking past vaccine exposure to current cancer cases containing the virus.
Prethinking:
Question type:
Strengthen - We need to find information that makes the researchers' hypothesis more believable. The hypothesis is that the 1960 contaminated polio vaccine was the source of SV40 virus found in mesotheliomas decades later.
Precision of Claims
The key claims involve timing (1960 vaccine contamination, decades later cancer), causation (vaccine as source of virus in cancer), and population exposure (who got the contaminated vaccine and later developed mesothelioma with SV40).
Strategy
To strengthen the hypothesis that the 1960 contaminated polio vaccine caused SV40 to appear in mesotheliomas decades later, we need evidence that creates a stronger connection between the vaccine and the cancer cases. This could include: timing evidence showing the vaccine came before the cancers, demographic evidence showing people who got the vaccine are more likely to have SV40-positive mesotheliomas, or evidence ruling out other sources of SV40 exposure.