Hicks, George L.
Cornell University Press, 1971
Buku Teks
Gough, Ian
Macmillan, 1992
Buku Teks
edited by Lorraine Eden
St. Martin's Press, 1993
Buku Teks
Balaam, David N., 1950-
Pearson/Prentice Hall, 2005
Buku Teks
Bagchi, Amiya Kumar
Cambridge University Press , 1984
Buku Teks