Which Statement Best Illustrates the Law of Diminishing Returns from Studying

Which statement best illustrates the law of diminishing returns from studying?

A) As hours of studying decrease, the student's GPA will also diminish.
B) As study hours increase, the amount of learning will increase at a diminishing rate.
C) Students with higher GPAs tend to study fewer hours on the night before a big exam.
D) Students who cram the night before a big exam do not show much improvement in their learning.