The requirements of knowing, understanding, mastering and using are getting higher and higher. From just knowing this content to being able to solve practical problems with the knowledge learned, there are generally such divisions in various curriculum outlines.

For learners, we can carry out targeted learning according to this requirement. For those who are not demanding, spend less energy, know or understand. For those who need to master or use it, we should learn it thoroughly, and study the principle, reasoning or scope of application thoroughly to meet the requirements of the curriculum standard.