6US Department of Health and Human Services. The health conse- quences of involuntary exposure tobacco smoke : a report of the Surgeon General : 2006 [ R ]. Washington DC : US Government Printing Office, 2006:1-7.
8BRESLAU N,PETERSON E L.Smoking cessation in young aduhs:age at initiation of cigarette smoking and other suspected influence[ J ].Am J Pub Health, 1996,86(2) :214-220.