The sentence ends having a string of "wh-" noun clauses. These clauses aren't concerns, so the final a person also needs to not be a matter. "Which a person could be the best" is clearly an issue format, so it is sensible that " Vitamin B-twelve is an important nutrient https://share.evernote.com/note/c1a29341-55fb-6549-054a-7664564039cf