The ancient Nubians inhabited an area in which typhus occurs, yet surprisingly few of their skeletons show the usual evidence...
GMAT Critical Reasoning : (CR) Questions
The ancient Nubians inhabited an area in which typhus occurs, yet surprisingly few of their skeletons show the usual evidence of this disease. The skeletons do show deposits of tetracycline, an antibiotic produced by a bacterium common in Nubian soil. This bacterium can flourish on the dried grain used for making two staples of the Nubian diet, beer and bread. Thus, tetracycline in their food probably explains the low incidence of typhus among ancient Nubians.
Which of the following is an assumption on which the argument relies?
Passage Analysis:
| Text from Passage | Analysis |
| The ancient Nubians inhabited an area in which typhus occurs, yet surprisingly few of their skeletons show the usual evidence of this disease. |
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| The skeletons do show deposits of tetracycline, an antibiotic produced by a bacterium common in Nubian soil. |
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| This bacterium can flourish on the dried grain used for making two staples of the Nubian diet, beer and bread. |
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| Thus, tetracycline in their food probably explains the low incidence of typhus among ancient Nubians. |
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Argument Flow:
We start with a medical mystery - why didn't ancient Nubians get much typhus despite living where it was common? Then we learn their skeletons contain tetracycline, which is an antibiotic. Next, we discover this antibiotic came from bacteria that grew on their grain, which they used to make their daily bread and beer. Finally, we conclude that eating this antibiotic-containing food protected them from typhus.
Main Conclusion:
Tetracycline in ancient Nubian food probably explains why they had low rates of typhus disease.
Logical Structure:
The argument uses the presence of tetracycline in Nubian remains, combined with the pathway from grain bacteria to food consumption, to explain the surprising absence of typhus. It's a cause-and-effect argument where regular antibiotic consumption through food prevented disease.
Prethinking:
Question type:
Assumption - We need to find what must be true for the author's conclusion to hold. The author concludes that tetracycline in Nubian food explains their low typhus rates.
Precision of Claims
The argument makes specific claims about causation (tetracycline caused low typhus), effectiveness (tetracycline can prevent/treat typhus), and consumption patterns (Nubians regularly consumed tetracycline through food).
Strategy
To find assumptions, we need to identify gaps in the logical chain from premises to conclusion. The argument jumps from 'Nubians had tetracycline in their skeletons' and 'tetracycline comes from bacteria on grain used for food' to 'tetracycline in food explains low typhus rates.' We need to find what must be true to make this jump valid.
This choice discusses whether tetracycline affects other infectious diseases besides typhus. However, the argument is specifically about explaining low typhus rates, not about tetracycline's broader effects. Whether tetracycline affects other diseases is irrelevant to the conclusion that it explains low typhus incidence. The argument doesn't require this to be true.
This identifies a critical gap in the argument's logic. The author concludes that tetracycline in Nubian food explains low typhus rates, but never addresses whether food preparation processes might have destroyed the antibiotic's effectiveness. If making bread and beer rendered tetracycline ineffective, then consuming these foods wouldn't have provided any disease protection. For the argument to work, we must assume the tetracycline remained active after food processing. This assumption is essential for the conclusion to be valid.
This statement about typhus transmission methods is not required for the argument. The argument claims tetracycline in food prevented or treated typhus, regardless of how people might have contracted it. Whether typhus spreads through contaminated food doesn't affect whether antibiotics in food could combat the disease once present. The argument can work without making any assumptions about transmission routes.
This choice makes the argument unnecessarily restrictive. The author only needs to show that bread and beer contained enough tetracycline to be protective - not that they were the exclusive sources. Even if other foods also contained tetracycline, the conclusion about bread and beer providing protection could still be correct. The argument doesn't require these to be the only tetracycline sources.
The fatality rate of typhus is irrelevant to the argument's logic. Whether typhus is generally fatal or not doesn't affect whether tetracycline could prevent or treat it. The argument is based on the observation that Nubians had low typhus rates, and this observation stands regardless of how serious the disease typically is. The argument works whether typhus is mild or severe.