Argument: Researchers found that people who drink green tea every day have lower rates of heart disease, and concluded that green tea protects the heart. Which of the following, if true, most strengthens the argument?
Correct answer A. The lower rate remained after accounting for differences in diet, exercise and smoking
Explanation
Ruling out diet, exercise and smoking removes other explanations, so the link to green tea becomes stronger. The option about exercise offers an alternative cause and weakens the conclusion.
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