take Huang-Huai-Hai region as an example take Lanzhou-Xining region as an example take the Yangtze River Delta region as an example taking the western region as an example 农地生产效率研究：以黄淮海地区为例：take Huang-Huai-Hai region as an example taking the northwest region as an example take Shanghai as an example take Wuling mountain area as an example take Guangdong and Guangxi as an example take Guangdong as an example