Cohen, Nathan Edward, author
National Ass. of Workker, 1964
Buku Teks
Healy, Karen, author
Palgrave Macmillan, 2005
Buku Teks
Martin, Ruben, author
Learning Matters, 2010
Buku Teks
edited by Jerrold R. Brandell
Free Press, 1997
Buku Teks
O`Sullivan, Terence, author
Macmillan, 1999
Buku Teks