If you develop a habit of studying a certain subject at a certain time ,you need less energy tofocus your attention upon it.You need not spend any time to think what to doat a certain time.

• 如果你养成了再一定时间里学习一定的功课的习惯，在这些功课上花费的精力就会减少，因为你不需要花时间考虑在这段时间该干什么。