Keller, kotler, author
Pearson Education, Inc, 2006
Buku Teks
Howard, John A., author
Richard D. Irwin, 1957
Buku Teks
Keegan, Warren J., author
Prentice Hall of India, 1982
Buku Teks
Rexroad, Robert A.
John Wiley & Sons, 1983
Buku Teks
Haas, Robert W
Kent, 1982
Buku Teks