Brown, F.E.
Addison-Wesley, 1980
Buku Teks SO
Cox, Eli P.
Harper & Row, 1979
Buku Teks SO
Hamburg, Morris
Harcourt Brace Jovanovich, Pub., 1991
Buku Teks SO
edited by Anthony G. McGrew
Manchester University Press, 1985
Buku Teks SO
Kotler, Philip
Holt, Rinehart and Winston , 1971
Buku Teks SO