Hammer, Darrel P.
Westview Press, 1990
Buku Teks
Rivoli, Pietra
John Wiley & Sons, 2005
Buku Teks
Wiarda, Howard J.
Hartcourt College Publishers, 2001
Buku Teks
Beer, Samuel H.
Alfred A. Knopf, 1966
Buku Teks SO
Brzezinski, Zbigniev K.
Frederick A. Praeger, 1962
Buku Teks