C: a demand characteristic

Incorrect.
Demand characteristics are cues from the experimenter, telling the participant(s) in the study what behaviors are expected or other factors in the setting of a study that influence the behavior of the participants.  For example, imagine that researchers from the University were coming to your home to correlate your media consumption.  You would probably not choose that particular evening to watch an X-rated film.  Information about children's TV viewing habits at home does not typically come from experiments, but instead involves people's self-reports of their own behavior.