"Knowledge is a treasure, but practice is the key to it."
参考范文：
In this constantly changing world, how to put the knowledge acquired every day into reality has intrigued numerous people. As a proverb goes, “ Knowledge is a treasure, but practice is the key to it.” Apparently, this saying aims to deliver the message that if we truly want to master the knowledge we learn, we ought not to stop practicing it.
第一段三句话，用核心词引入+带出引言+引言的目的
There are several reasons accountable for this statement. To begin with, human being are forgetful beings; therefore, only when we use knowledge, make mistakes, and try to use it again will we be able to remember it by our heart. Moreover, knowledge has become growingly complicated and we can seldom genuinely grasp the essence of it if we do not practice it and ponder it over again and again. For instance, there used to be simple diseases, such as the cold and measles, and a doctor might have the knowledge to treat all the common ones. However, with our living environment becoming ever increasingly harsher, the diseases have evolved into weird, irremediable, and unpredictable ones. Therefore, the medication has been divided into numerous branches, and doctors of each one have to practice for years only in order to cure the diseases belonging to the similar sort.
第二段，解释引言。中心句+两个原因+举例。举例应用对比法。
Practicing, to sum up, is of greatest importance for those who are determined to learn knowledge well. Not only does it assist people to remember knowledge better, but we are able to catch up with the speed of the evolotion of knowledege. As a student, I hope that the young can focus more attention on practicing what they learn than on remembering it blindly so that the knowledge will become our real treasure and make our life more splendid.
第三段，总结该引言的合理+两个理由+展望未来。