8Babbie,E.The Basics of Social Research.Belmont CA:Wadsworth Publishing Company,1999.
9Buck,W.Sociology and Modern Systems Theory.Englewood Cliffs,N.J.:Prentice-Hall,1967.
10Collins,M.E.Transition to Adulthood for Vulnerable Youths:A Review of Research and Implications for Policy.Social Service Review,No.75,2001,pp271-291.