Final answer:
The opportunity cost principle is the best argument against the claim that longer movies always offer more benefit; it implies the value of a movie is relative to other activities one could engage in instead.
Step-by-step explanation:
The best argument against the claim that longer movies provide more benefit than shorter movies, based on the scenario provided, is a. opportunity cost principle. This principle suggests that the length of the movie does not inherently determine its value. Instead, it is the quality of the experience relative to other possible uses of one's time. For instance, in Selena's scenario, continuing to watch a movie that she finds terrible represents an opportunity cost, namely the loss of something she could be doing instead that would offer greater satisfaction or benefit. Thereby, her decision should be based on weighing the marginal costs and benefits of her current and future options rather than just considering the sunk cost of the movie ticket.