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.