Marginal Thinking Is Best Demonstrated By

Marginal thinking is best demonstrated by:

A) choosing to spend one more hour studying economics because you think the improvement in your score on the next quiz will be worth the time sacrificed.
B) deciding to never purchase a coat made of animal skin or fur.
C) acquiring all information relevant to a choice before making that choice.
D) measuring all the costs of a meal against all its benefits when deciding on whether to order a second milkshake.
E) deciding to never buy an airline ticket during the holiday period.