Could you explain the origin of the Double Ninth Festival?

你能解释一下重阳节的起源吗？

同一单元的其他句子

• The Spring Festival is the most important traditional holiday in China.春节是中国最重要的传统节日。
• During the Lantern Festival, people hang colorful lanterns in the streets.元宵节期间，人们在大街上挂起五彩缤纷的灯笼。
• Have you ever participated in a dragon boat race during the Dragon Boat Festival?你参加过端午节期间的龙舟比赛吗？
• Families gather together to enjoy a reunion dinner on New Year's Eve.除夕夜，家人聚在一起吃团圆饭。
• The Mid-Autumn Festival is celebrated with mooncakes and admiring the full moon.中秋节以吃月饼和赏满月来庆祝。