The Sentence ends having a string of "wh-" noun clauses. These clauses will not be questions, so the final a person also needs to not be a question. "Which just one could be the best" is clearly an issue structure, so it is sensible that " Vitamin B-12 is an https://share.evernote.com/note/f5ed0f3d-3352-3d51-727d-10fa609eb157