The law of over－learning explains why cramming (突击学习) for an examination, though it may result in a passing grade, is not a ________ way to learn a school course.[ ]

A. convenient  

B. demanding

C. satisfactory

D. swift

如果在表面处理前或表面处理中，对装配或设计缺陷进行修复，涂料性能将会好得多（因此就长效而言也就更为经济）