Gormley, William T., author
CQ Press, 2004
Buku Teks
Woll, Peter, author
Little, Brown , 1986
Buku Teks
edited by Richard M. Ketchum
Dutton, 1955
Buku Teks
Greenberg, Edward S., author
Pearson/Longman, 2005
Buku Teks
Ross, Alf, author
Harvard University Press, 1952
Buku Teks