I saw a comment saying: Among the ten heavenly stems, A, B, E, Geng and Ren are yang, B, Ding, Ji, Xin and Gui are yin; among the twelve earthly branches, Zi, Yin, Chen, Wu, Shen, and Xu are yang, Chou, Mao, Si, Wei, You, and Hai are yin. The eight characters are composed of four heavenly stems and four earthly branches. If these eight characters are all feminine or masculine, it is called The eight characters are pure yin or pure yang.
Heavenly Stems: Xin, Ding, Gui, Yi and Earthly Branches: You, You, Si, and Mao all belong to "Yin", so how can you say it is not pure Yin?