Our ancestors defined the 24 solar terms of a year as A, Xia, B, Shang, C, Chun Qiu and D.

Test Analysis: This question mainly examines the relevant historical facts of China's ancient calendar. According to what we have learned, the development of ancient calendars in China is closely related to agriculture. Today's lunar calendar, also known as the "summer calendar", originated in the Xia Dynasty. By the Shang Dynasty, the calendar was gradually complete. During the Warring States period, in order to arrange agricultural production, people decided to have 24 solar terms a year, so D fits the question.