McIver, Colin
Longman , 1972
Buku Teks
Randall, Geoffrey, author
Crest Publishing House, 2001
Buku Teks
Morse, Stephen A., author
McGraw-Hill , 1967
Buku Teks
Kotler, Philip, author
[publisher not identified], [date of publication not identified]
Buku Teks
Kotler, Philip, author
Prentice-Hall, 2000
Buku Teks