Funding for this research was provided by:
the Educational Commission of Zhejiang Province (Y201840779)
Research Funded Project of Sichuan Provincial Department E- ducation (18ZB0007)
Text and Data Mining valid from 2019-08-13
Received: 25 April 2019
Accepted: 11 July 2019
First Online: 13 August 2019
: The authors declare that they have no competing interests.