Ryan, William T
Richard D. Irwin, 1980
Buku Teks
Ryan, William T.
Dew Jones Irwin, 1980
Buku Teks
Ryan, William T.
Richard D. Irwin, 1981
Buku Teks
Ryan, William T.
Learning System Company, 1971
Buku Teks
Kotler, Philip, author
Prentice-Hall, 1996
Buku Teks