A class in marketing designs two videos advertising an expensive Mercedes sports car. They test the videos by asking fellow students to view both (in random order) and say which makes them more likely to buy the car. Mercedes should be reluctant to agree that the video favored in this study will sell more cars because
(a) There is no control group.
(b) There is no placebo.
(c) The study used a matched pairs design instead of a completely randomized design.
(d) This is an observation study, not an experiment.
(e) Results from students may not generalize to the older richer customers who might buy a Mercedes.