Answer: c. Choosing to spend one more hour studying economics because you think the improvement in your score on the next quiz will be worth the sacrifice of time
Explanation: The word marginal means evaluating the benefits of an activity over the cost of doing that activity. In other word, it requires the individuals to weigh the benefits of doing something over its cost. If the benefits exceed cost it is best to do that activity. So, choosing to spend one more hour studying economics because you think the improvement in your score on the next quiz will be worth the sacrifice of time involves marginal thinking.