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

Moe divides his time between studying Physics and studying Economics. His production possibilities curve for his final grade in each class is shown below. According to Moe’s PPC, moving from a 70 to an 80 in economics:
A.has a higher opportunity cost than moving from an 80 to a 90.
B.is unattainable.
C.has a lower opportunity cost than moving from an 80 to a 90.
D.is inefficient.
正确答案：has a lower opportunity cost than moving from an 80 to a 90.