The law of overlearning explains why cramming (突击学习) for an examination, though it may result in a passing grade, is not a satisfactory way to learn a college course. By cramming, a student may learn the subject well enough to get by on the examination, but he is likely soon to forget almost everything he learned. A little overlearning, on the other hand, is really necessary for one's future development.
What is the author's opinion on cramming?

A．It leads to failure in college exams.

B．It's helpful only in a limited way.

C．It's possible to result in poor memory.

D．It increases students' learning interest.