Suppose That You Are Spending Two Hours a Day Studying

Suppose that you are spending two hours a day studying economics, and your grade is 85 percent. You want a higher grade and decide to study for an extra hour a day. As a result, your grade rises to 90 percent. Your marginal benefit is the

A) 5 point increase in your grade minus the opportunity cost to you of spending the hour studying.
B) extra hour per day you spend on studying.
C) three hours per day you spend on studying.
D) 5 point increase in your grade.