Final answer:
The opportunity cost of attending the party is the most desirable alternative foregone, which is study time if that was the next best option valued by the decision-maker over going to a movie.
Step-by-step explanation:
The question involves understanding the concept of opportunity cost in economics. Opportunity cost refers to the most desirable alternative that is foregone when a choice is made. In the scenario presented, since you have chosen to attend the party, your opportunity cost is the next best alternative you would have chosen if you did not go to the party. If studying for the test was your next best alternative, then that represents the opportunity cost. The fact that you could go to a movie any time does not exclude studying from being an opportunity cost, as opportunity cost depends on what you, the decision-maker, value more at the time of the choice.
Considering that, the correct answer to the question "A test is scheduled for Monday morning, but you went to a party on Saturday night. If you hadn't attended the party, you could have studied for the test or gone to a movie. Which of the following sentences is true?" is:
d. Because you could go to the party only that night but could go to a movie any time, the opportunity cost of the party is the study time.