Teacher Guo Huanan is very good, and his lectures are humorous, involving hidden mathematical laws in after-school and life. Moreover, Mr. Guo has a certain age and higher qualifications. I remember once listening to him talk about permutation and combination, and he actually pointed out the solution to this problem in the primary school Olympic Games. I remember once listening to his compilation, he actually inserted the habit of playing word games in China. The classroom is rich in content, often interacts with students, and the topic thinking is open. Listening to this gentleman's lecture must be like spring breeze.