No.1 is a UP expert who specializes in high school and junior high school mathematics. He speaks very seriously, corresponding to each chapter of the textbook, which is very easy to understand. You can watch his math videos, and they are all free. Billie Billie's main name is Zhang Yi, and Billie Billie's full name is Bi Li Bi Li. Bi Li Bi Li is a highly concentrated cultural community and video platform for young people in China, which is affectionately called "Bili Bili" by fans. The biggest feature of the beep is the real-time comments suspended above the video, which is also the "barrage". This is the second website in Chinese mainland that provides this function.