Study of ecological environment during the Qin and Han dynasties 并列题名：Study of ecological environment during the Qin and Han dynasties a study on the legal system of foreign trade during the ming and qing dynasties Study on the development of Zhongyuan towns during the Ming and Qing Dynasties The living environment culture of Qin and Han Dynasties 并列题名：The living environment culture of Qin and Han Dynasties Study on the ecological environment of the central plains during the Shang dynasty Study on the change of ecological environment in Northeast China in Qing Dynasty Governance of ecological environment in wind gap regions of mega-cities a study on the temples of Three teachings in Zezhou during the Ming and Qing dynasties