Schumaker, Paul
Blackwell Publishing, 2008
Buku Teks SO
Tannenbaum, Donald G.
Wadsworth/Thomson learning, 2004
Buku Teks SO
edited by Thomas Christiano and John Christman
John Wiley & Sons, 2007
Buku Teks
Pojman, Louis P.
McGraw-Hill , 2003
Buku Teks SO
Pojman, Louis P.
McGraw-Hill , 2003
Buku Teks SO