the answer to your question is A. Ethos. it is one of the techniques in persuasion, people tend to listen to those who are professionals and have authority in some fields. in your case dentists know more about chewing gum so they are more convincing and more respected ad we tend to listen to them. Logos is more logical and fact base, most popular in this case of persuasion is using statistics and facts. Pathos is more of an emotional type of persuasion, it can play on fear, sadness and etc.
