Funding for this research was provided by:
National Educational Examination Center (GJK2017046)
Received: 29 July 2019
Accepted: 17 May 2020
First Online: 24 May 2020
Ethics approval and consent to participate
: The study was granted an exemption from requiring ethics approval by the Peking University Institutional Review Board because the survey and tests did not include sensitive questions. An introduction about the survey was provided on the first page of the questionnaire, including aims, the main contents of this survey. The sampled students had the right to withdraw at any time.
: Written proof of exemption from research ethics review was obtained from Peking University. A copy of the proof is available for review by the Editor of this journal.
: The authors declare that they have no competing interests.