The author makes a subtle leap in their argument, and I actually missed it until I read B. The author makes an argument about heart disease. Everything is about the relationship between fat, wine, and heart disease. However they then shift in the conclusion to discussing general health. It's possible that a minor decrease in the risk of heart disease would be more than offset by a major increase in the risk of liver disease. This is what b gets at. I think that being more critical of the argument itself will help you to immediately see why b looks good.