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Article History

Received: 5 September 2017

Accepted: 18 February 2019

First Online: 28 February 2019

Ethics approval and consent to participate

: This study was approved by Ethical Review Committee of Chinese Academy of Medical Sciences. Written informed consent was obtained from all participants before the study. The participants were informed of the main purpose of this investigation and their answers related to any personal information would be kept strictly confidential and would not be disclosed to any government departments, private institution or others.

: Not applicable.

: The authors declare that they have no competing interests.

: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.