2. Later, there appeared seven tones of "Gong, Shang, Semi-Shang, Jiao, Zheng, Semi-Zheng and Yu".
3. The reason why pentatonic scale is dominant is related to the characteristics of Chinese civilization. I suggest you listen to Tsinghua University's excellent course "Cultural Relics and Culture China I: Jia Hu Bone Flute and Ancient Seven Tones in China".
4. Please refer to "A Brief History of China Music" Southwest Normal University Press; The second edition (July 2008 1) was published; A brief history of ancient music in China, first edition in June 2002.