A. D. is the abbreviation of "Gregorian calendar era", which is an international calendar system.

Take the legendary birth year of Jesus Christ as the first year of the Gregorian calendar.

(equivalent to the first year of the Western Han Dynasty in China).

In A.D. 1 year, China's "Fan Sheng Zhi Book" put forward the principles of dry land cultivation, such as interesting time and early hoeing, and other cultivation techniques, such as equal ear selection, manure juice and drug seed dressing.

In fact, the year when Jesus was born should be a few years BC.

"After Zhao (who reigned 73 to 48 years ago) implemented the policy of" sharing interest with the people "for 38 years, the national strength increased, but at the same time, the local power also increased, which seriously affected the rule of the Han Empire, from (reigned 48 to 32 years ago) to (reigned 32 to 8 years ago) and mourned the emperor (. When Liu Ying ascended the throne, North Korea's power had fallen into the hands of Wang Mang's consorts. In the eighth year, Wang Mang usurped the throne and changed his title to a new country. At this point, the Western Han Dynasty's rule over China came to an end. "