Gregorian calendar 20 15 September 1 is the last year of B, the month of Shen Jia and Chen Geng. How is this worked out?

Heavenly stems and earthly branches is referred to as the main cadre. A, B, C, D, E, Ji, Geng, Xin, Man and Ghost are collectively called Ten Heavenly Branches, while Zi, Ugly, Yin, Mao, Chen, Si, Wu, Wei, Shen, You, Xu and Hai are collectively called Twelve Earthly Branches. Heavenly stems and earthly branches constitutes the ancient calendar year. In folklore, people think that the sky is dry, which corresponds to some omens. Ten branches and twelve branches are matched in turn, forming sixty basic units and forming a set of sub-disciplines.

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