D: The salesperson's credibility is enhanced.

Remember that this is an ad, and the person wearing the doctor’s coat is an actor. This is a case of misattribution.

Attribution is the process by which people use information to make inferences about the causes of behavior or events. Simply put, this is how we go about inferring behavior (our own and those of others).

Misattribution is attributing an event to something with which it really has no connection or association. It's making an incorrect attribution.

When we see an ad with an actor wearing a doctor’s coat, most people incorrectly infer that the person has some special medical knowledge. Therefore this is a case of misattribution.