Submitted on: 11 January 1999.
Revised on: 31 January 1999.
Accepted on: 20 February 1999.
___________________Archives of Public Health---BMC
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http://reply.papertrans.cn/1/26/2546/2546-33.png
Submitted on: 22 July 2020.
Revised on: 30 August 2020.
Accepted on: 26 October 2020.
___________________Archives of Public Health---BMC
http://reply.papertrans.cn/1/26/2546/2546-35.png
Submitted on: 14 October 2018.
Revised on: 03 November 2018.
Accepted on: 17 November 2018.
___________________Archives of Public Health---BMC