1. Department of Economics Teaching and Research, Party School of the Central Committee of C.P.C (National Academy of Governance), Beijing 100091, China
2. School of Humanities and Social Sciences, Beijing Institute of Technology, Beijing 102488, China
3. Institute of Advanced Agricultural Sciences, Peking University, Weifang 261325, China
4. Leibniz Institute of Agricultural Development in Transition Economies, 06120 Halle, Saale, Germany