The meaning of a, b and d, and the origin of a, b and d.

1, a, b, c and d are heavenly stems, which are used to arrange the year and date. It was founded in 2697 BC. Pronunciation is A(Jiǐ), B(yǐ), C(Bǐng) and D(Dοng).

2. Heavenly stems refer to the ten heavenly stems in heavenly stems and earthly branches. The original ten-day dry said: "encounter, enlightenment, softness, strength, harmony, tu Wei, admiration, emphasis, mystery, release." The simplified heavenly stems say: "A, B, C, D, E, G, G, G, G".

3. The five elements of Tiangan are divided into yin and yang, specifically: Jiamu, Mu Yi, Huhuo, Ding Huo, Wutu, Jitu, Gengjin, Jin Xin, Renshui and Guishui, in which methyl propyl valerate is positive and ethyl butyl hexin decyl is negative.