Choose one or two simple questions as the beginning and solve them in about 5 minutes. Choose a few questions with moderate difficulty, which are suitable for more than 50% of students. The explanation method is classic, or it is acceptable according to the usual experience. Finally, it is better to put two big finale questions, which are more difficult, but after the explanation, people will suddenly feel that this topic is simple, that is, the explanation method of this topic is not common, and the overall effect will come up with a little brain teaser.