Today, I checked on the Internet, only to find that the lecturer, Mr. Teng Yanfeng, passed away in June 2009. I want to commemorate him here. This teacher is very dedicated in his lectures. I have watched many online videos of distance education. Teacher Teng has a charming smile, clear words and vivid teaching. The teaching video of this circuit is the only one that keeps me awake after watching it. Admire this conscientious and good teacher! Teacher Teng, have a good trip!