@TekenaAbere furthermore eating the same amount of iron doesn’t take away from the claim that eating less can reduce the chance of getting the disease.

I think i understand it now. Choice A is worded in a difficult way. It’s basically saying people with the genetic predisposition have the SAME amount of iron in their diets as people without the predisposition. So therefore we can rule out that any genetic factors are the cause of the disease. This doesnt tell us too much about iron but it does let us know that its not a genetic or other factor causing Parkinson’s so it therefore strengthens the argument.