Blanchard, Wendell
Buku Teks
edited by Anthony Milner and Mary Quilty
Oxford University Press, 1997
Buku Teks
by Jack Bavington
Maclean-Hunter Learning Materials, 1976
Buku Teks
Downs, James F.
Glencoe Press, 1975
Buku Teks
Mort, Frank
Routledge, 1996
Buku Teks