Snowden, Lynne L.
Pearson-Prentice Hall, 2005
Buku Teks
Cox, Harold
Prentice-Hall, 1984
Buku Teks SO
Kennan, George F., 1904-
Princeton University Press , 1954
Buku Teks SO
Newsom, Doug
Wadsworth and Cengage Learning, 2013
Buku Teks SO
Draper, Theodore
Frederick A. Praeger, 1962
Buku Teks SO