Funding for this research was provided by:
Beijing Municipal Social Sciences Key Project (15ZDA46)
Beijing Municipal Commission of Education (15ZDA46)
Ministry of Education Humanities and Social Sciences Planning Fund Project (14YJA790075, 14YJA790075)
Article History
First Online: 9 December 2019
Compliance with ethical standards
:
: The Authors declare that they have no conflict of interest.
: This article does not contain any studies with human participants or animals performed by any of the authors.