Moe Divides His Time Between Studying Physics and Studying Economics

Multiple Choice

Moe divides his time between studying Physics and studying Economics.He has discovered that he can earn grades as shown on this production possibilities curve.
Refer to the figure above.According to Moe's PPF,moving from a grade of 80 in economics to a grade of 90 in economics:

A) is inefficient.
B) comes at a lower opportunity cost than moving from a 90 to a 100 in economics.
C) is not feasible.
D) comes at a higher opportunity cost than moving from a 90 to a 100 in economics.