Complex sentence: Jiutian Xuannü appears at least three times in the "Classic of the Yellow Courtyard", where the adept is instructed to send down his breath to enter the goddess' mouth.
Split into simpler sentences: Jiutian Xuannü appears at least three times in the "Classic of the Yellow Courtyard". In the work, the adept is instructed to send down his breath to enter the goddess' mouth.