A certain tropical island received food donations in the form of powdered milk for distribution to its poorest residents, who...
GMAT Critical Reasoning : (CR) Questions
A certain tropical island received food donations in the form of powdered milk for distribution to its poorest residents, who were thought to be malnourished. Subsequently, the rate of liver cancers among those islanders increased sharply. The donated milk was probably to blame: recent laboratory research on rats has shown that rats briefly exposed to the substances aflatoxin tend to develop liver cancer when fed casein, a milk protein.
Which of the following most logically completes the passage?
Passage Analysis:
| Text from Passage | Analysis |
|---|---|
| A certain tropical island received food donations in the form of powdered milk for distribution to its poorest residents, who were thought to be malnourished. |
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| Subsequently, the rate of liver cancers among those islanders increased sharply. |
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| The donated milk was probably to blame: recent laboratory research on rats has shown that rats briefly exposed to the substances aflatoxin tend to develop liver cancer when fed casein, a milk protein. |
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Argument Flow:
The argument starts with background context (milk donation to malnourished islanders), then presents a concerning outcome (sharp increase in liver cancer), and finally proposes an explanation (the milk caused it) backed by laboratory research on rats.
Main Conclusion:
The donated powdered milk was probably responsible for the sharp increase in liver cancer rates among the islanders.
Logical Structure:
The author uses a causal argument structure: since liver cancer rates increased after milk distribution, and since lab research shows that aflatoxin exposure plus casein (milk protein) causes liver cancer in rats, the author concludes the donated milk likely caused the cancer increase in humans. The rat study serves as analogical evidence to support the causal claim.
Prethinking:
Question type:
Logically Completes - We need to find what makes the rat study relevant to the island situation
Precision of Claims
The argument claims milk caused increased liver cancer rates, supported by rat studies showing aflatoxin + casein leads to liver cancer
Strategy
For logically completes questions, we need to bridge the gap between the evidence provided (rat study) and the conclusion (milk caused cancer in islanders). The rat study shows aflatoxin + casein = liver cancer, so we need scenarios that connect this finding to the island situation. What would make this rat study actually relevant to blaming the donated milk?
This choice establishes that islanders were likely exposed to aflatoxin through peanuts, a staple food that supports aflatoxin-producing mold in tropical climates. This creates the crucial link between the rat study and the island situation - if islanders regularly consumed aflatoxin from peanuts and then added casein from donated milk to their diet, they would experience the same aflatoxin + casein combination that caused liver cancer in rats. This makes the rat research directly relevant to explaining the increased cancer rates. This choice completes the logical bridge needed.
This choice discusses the liver's sensitivity to carcinogens compared to other organs. While this might explain why liver cancer specifically increased, it doesn't establish the connection between the rat study findings and the island situation. The rat study's relevance depends on showing that islanders had aflatoxin exposure, not on explaining why the liver is particularly vulnerable. This doesn't make the rat study relevant to the specific situation.
This choice points out that milk contains proteins other than casein. However, this information doesn't help explain why the rat study is relevant - in fact, it might weaken the connection since the rat study specifically focused on casein's role. We need to show why the rat findings apply to the islanders, not introduce additional complexity about other milk proteins. This doesn't establish relevance and may actually complicate the argument.
This choice discusses the appropriateness of powdered milk for tropical destinations. While this might be practically relevant information, it doesn't explain why the rat study findings about aflatoxin + casein causing liver cancer are relevant to the island situation. The form of milk delivery doesn't connect to the biological mechanism studied in rats. This is irrelevant to making the rat study applicable.
This choice mentions that milk recipients were screened for their ability to digest milk. Like Choice D, this addresses a practical consideration but doesn't establish the connection between the rat study and the island situation. The ability to digest milk doesn't relate to the aflatoxin + casein interaction that caused liver cancer in rats. This doesn't make the rat research relevant to the cancer increase.