Funding for this research was provided by:
Natural Science Foundation of Shandong Province (ZR2019BG006)
Project for Humanities and Social Sciences Research of Ministry of Education of China (19YJC630149)
Shandong Provincial Higher Educational Social Science Program of China (J18RA053)
Article History
Received: 30 March 2020
Revised: 2 June 2020
Accepted: 12 June 2020
First Online: 28 July 2020
Compliance with Ethical standards
:
: The author declares that there are no conflicts of interest regarding the publication of this paper.