This is an actual participant who has agreed to participate in a research study, but is not aware that deception is being used to conceal the real purpose of the experiment.

A) confederate
B) actor
C) experimental subject
D) naïve subject

A naïve subject is an individual who agrees to participate in a research study but is not aware that deception is being used to conceal the real purpose of the experiment. This is the most appropriate choice for the scenario described. A confederate is a member of the research team who pretends to be a participant, an actor is someone who is intentionally playing a role in the study, and experimental subjects are participants who are aware of the true purpose of the experiment.