Roskin, Michael G., author
Pearson/Prentice Hall, 2004
Buku Teks
Bull, Hedley, author
Macmillan, 1995
Buku Teks
Miller, Lynn H., author
Westview Press, 1985
Buku Teks
Rourke, John T., author
Brooks/Cole, 1986
Buku Teks
edited by Burns H. Weston
Transnational , 1994
Buku Teks