Julia's Total Benefit from Taking Four University Courses Is $10,000

Julia's total benefit from taking four university courses is $10,000. If she takes a fifth course, her total benefits increase to $12,000. Julia should take this fifth course only if her

A) total costs are less than $10,000.
B) additional costs are less than $2,000.
C) additional costs are less than $2,400.
D) total costs are less than $12,000.
E) course is free.