Choice B

@Meredith, (B) is incorrect because it has no impact on the validity of the conclusion. Just because other dietary changes may result in similar reduction in risk of heart disease does not disprove the fact that the consumption of vitamin C supplements lowers the risk of heart disease as well. The correct answer choice needs to either weaken the premise and demonstrate that the conclusion of the study is incorrect or weaken the conclusion directly and demonstrate that people who consume vitamin C supplements are not healthier on average despite the heart-disease related benefits. Let me know if you have any further questions.