Necessary AssumptionDiff: Easy
Logic Breakdown
Passage Summary: Doctors test for TB by putting TB proteins under your skin. If your body recognizes them, it reacts. Doctors assume that if your skin reacts, it's definitely because you've had TB.
Conclusion: A skin reaction to injected tuberculosis proteins proves that a person has been infected with the disease.
Reasoning: The immune system of an infected person recognizes these specific proteins and triggers an inflammatory response at the site of the injection.
Analysis: The physicians are assuming a perfect correlation between the skin reaction and a TB infection. To make this argument work, they must assume that nothing else can cause that specific skin irritation. If a different bacterium or a general allergy to the injection itself could cause the same reaction, the test would produce 'false positives.' Look for an answer that confirms the reaction is unique to tuberculosis exposure.
Conclusion: A skin reaction to injected tuberculosis proteins proves that a person has been infected with the disease.
Reasoning: The immune system of an infected person recognizes these specific proteins and triggers an inflammatory response at the site of the injection.
Analysis: The physicians are assuming a perfect correlation between the skin reaction and a TB infection. To make this argument work, they must assume that nothing else can cause that specific skin irritation. If a different bacterium or a general allergy to the injection itself could cause the same reaction, the test would produce 'false positives.' Look for an answer that confirms the reaction is unique to tuberculosis exposure.
Passage Stimulus
Passage Redacted
Unlock Full Passage6.Which one of the following is an assumption on which the physicians' reasoning depends?
Correct Answer
C
The test’s logic needs the reaction to be specific to prior TB infection. If TB proteins could trigger the same reaction due to something other than prior TB infection, the inference from reaction to infection would be invalid. Negation test: if the TB proteins’ ability to trigger the reaction is not exclusive, people without prior TB infection could still react—destroying the argument.
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