Artikel Jurnal
Craig, Garce J.
Prentice-Hall, 1992
Buku Teks SO
Turner, Jeffrey S., author
Harcourt Brace College, 1995
Buku Teks SO
Turner, Jeffrey S., author
Holt, Rinehart and Winston, 1987
Buku Teks SO
Zanden, James W. Vander, author
McGraw-Hill, 1993
Buku Teks SO