Funding for this research was provided by:
Natural Science Foundation of Hunan Province (2019JJ50382)
China Postdoctoral Science Foundation (2020M670473)
Youth Project of Humanities and Social Sciences of Ministry of Education in China (18YJC630213)
Key Project of Hunan Education Department (19A292)
National Social Science Foundation of China (19CGL030)
Received: 18 January 2020
Accepted: 23 September 2020
First Online: 2 October 2020
Ethics approval and consent to participate
: The submitted paper has not been published previously, is not under consideration for publication elsewhere, its publication is approved by all authors and tacitly or explicitly by the responsible authorities where the work was carried out.
: If accepted, it will not be published elsewhere in the same form, in English or in any other language, including electronically without the written consent of the copyright-holder.
: The authors declare that they have no competing interests.