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Article History

Received: 23 February 2018

Accepted: 30 May 2018

First Online: 14 June 2018

Ethics approval and consent to participate

: The health and family planning commission of Hebei province approved this study (Permit Number: 20150072). The research team explained the purpose of this study to middle school teaching management departments as well as adolescents of two middle schools. Parental/guardian written informed consent was obtained for participants under the age of 16 years old. As soon as consent was granted from the school leaders, parents and students, the researchers guided the adolescents about how to complete the questionnaires.

: All authors have read and approved the final draft of the manuscript.

: The authors declare that they have no competing interests.

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