1. College of Finance and Statistics, Hunan University, Lushan Rd., Changsha 410079, China
2. College of Finance and Statistics, Hunan University, Lushan Rd., Changsha 410079, China (Corresponding author), e-mail: einden855@163.com, https://orcid.org/0000-0003-4283-4954
3. Operating Branch of Nanning Rail Transit Group Co., Ltd., No. 69 of Yunjing Rd., Nanning 530029, China