I think D best supports the theme of the text.
Think about what a claim is. a claim is something that you state, even if you don't have proof. choice C is a fact, not a claim--it would be used as evidence to support a claim, but it doesn't serve as a claim itself.
i would say that B is the most appropriate claim to argue that people should be more nutritionally knowledgeable. choice D is almost a counterargument, in a sense, because it lists a flaw with food labels. choice A is a statement, but it can be proven with evidence--one could look at a food label to search for the listed items.
