Herriott, Luke
Rockport publishers, Inc., 2009
Buku Referensi
Fakultas Filsafat Universitas Katolik Santo Thomas, 2002
Majalah, Jurnal, Buletin
Farrelly, Lorraine
Wiley-Academy, 2003
Buku Teks SO
Sussman, Art
Jossey-Bass , 2006
Buku Referensi
Simmons, Christopher, 1973-
Rockport, 2006
Buku Referensi