All of the options listed—Media Relations, Interviews, Public Relations, and Advertising—are typically considered fields of external communication. However, if you are looking for the option that is least aligned specifically with external communication, "Interviews" might be the best choice. Although interviews can be a part of media relations or public relations strategies, they are not a distinct field of external communication like the others.
If the question is strictly asking for a field of external communication, none of the options would be correct since all can be associated with external communication in some capacity. If you're looking to identify which one is less of a formalized field, then "Interviews" could be your answer.