1. School of Economics and Management, Beijing University of Posts and Telecommunications, Beijing, P.R. China;
2. The Center of Industrial Economics and Green Development, Beijing University of Posts and Telecommunications, Beijing, P.R. China;
3. School of Statistics, Southwestern University of Finance and Economics, Chengdu, P.R. China;
4. Department of Commerce, Federal Urdu University of Arts, Sciences & Technology, Islamabad, Pakistan