We are given two factors that impact the risk of premature heart disease: endothelial cell reactivity and platelet adhesiveness. We see that grape juice has a positive effect on one of these factors (platelet adhesiveness). If grape juice had a positive effect on the other factor (endothelial cell reactivity), then this would strengthen the author’s position that the healthful effects of wine may be a result of natural compounds found in grapes.

The author’s argument about the healthful effects of wine depends on differentiating wine from other forms of alcohol, because the author claims that the benefits of wine may come from compounds found in grapes (and that these compounds wouldn’t be present in other forms of alcohol). Because of this, information that shows wine and beer having similar impacts does not strengthen the author’s position.

Additionally, according to the passage, a benefit of wine comes from the fact that wine may help prevent damage from high lipid levels. The information that wine and beer drinkers have similar lipid levels certainly doesn’t strengthen the author’s argument.

According to P3, individuals who drink lots of grape juice have a decrease in platelet adhesiveness. The author uses this finding to support the position that the benefits of wine may come from grapes. By suggesting that grape juice is actually correlated with higher platelet adhesiveness, (C) contradicts the finding from P3 (and actually relates grape juice with a risk factor for premature heart disease), so (C) would not strengthen the author’s position.

The question is whether moderate wine consumption is beneficial compared to no wine consumption; the passage is not concerned with comparing moderate and excessive wine consumption, so this wouldn’t strengthen the author’s position.

The author’s position is that wine consumption has healthful effects that may come from grapes; this information about genetic differences does not impact the author’s argument about the effects of wine consumption.