Received: 23 October 2017
Accepted: 30 May 2018
First Online: 13 June 2018
Ethics approval and consent to participate
: This study was approved by the Institutional Review Board (IRB) of Changsha Medical University. Informed written consent was obtained from the students who agreed to participate in this study, and their participation was voluntary. Permission was obtained from school authorities to conduct the study.
: The authors declare that they have no competing interests.
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