The answer is B.ethos.
Let's first look into the options:
Ethos- appeal to ethics.
By using ethos, the people use authority or credibility to peesuade people.
Pathos- appeal to emotions
By using pathos, people use audience’s sympathy or empathy to persuade them, such as using stories and photos to stimulate emotions.
Logos- appeal to logic
By using facts and figures, people are persuaded to believe the reason.
In this case, ethos is used as dentists are authorities.
Hope it helps!