Answer:
D. As a doctor, I have seen many similar cases, this is nothing new.
Explanation:
An ethos appeal simply confirms or reaffirms the credibility of the writer or speaker by showing that they're an authority on a given subject and should be listened to, which in turn can sway arguments.
Therefore, the sentence that most clearly makes an ethos appeal is option C.
This is because, he confirms his credibility as a doctor and thus, knows what he's doing.
