Behavioral Scientists Who Take the Role of Expert Witness in a Court

Behavioral scientists who take the role of expert witness in a court case might face an ethical dilemma because

A) legal norms hold that they should advocate for a particular position whereas scientific norms hold that they should be objective.
B) the American Psychological Association's ethical guidelines generally prohibit researchers from being expert witnesses.
C) being an expert witness requires one to take on the societal mentor role, a role that most researchers think is inappropriate.
D) of any of the above reasons.