A study found that regular consumption of dark chocolate is associated with a lower risk of heart disease. The researchers concluded that a specific antioxidant found in dark chocolate is responsible for this effect. Which of the following, if true, would most seriously weaken this conclusion?
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A
Participants in the study who ate dark chocolate regularly also reported exercising more frequently than those who did not.
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B
The study was funded by a company that produces dark chocolate.
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C
Milk chocolate, which has lower levels of the antioxidant, was not associated with a lower risk of heart disease.
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D
The antioxidant in question can also be found in other foods, such as berries and green tea.