A study finds that people who own pets live longer on average. A columnist concludes: 'Get a pet to live longer.' What is the most significant flaw?
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A
Healthier, more active people may be more likely to own pets, reversing the causal direction
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B
The study did not specify which types of pets were studied
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C
Longevity data is notoriously difficult to collect
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D
The columnist has a financial interest in pet ownership