Moe Divides His Time Between Studying Physics and Studying Economics

Multiple Choice

Moe divides his time between studying Physics and studying Economics. His production possibilities curve for his final grade in each class is shown in the accompanying figure. According to Moe's PPC, moving from a 70 to an 80 in economics:

A) is inefficient.
B) has a lower opportunity cost than moving from an 80 to a 90.
C) is unattainable.
D) has a higher opportunity cost than moving from an 80 to a 90.