Kegley, Charles W. (Charles William), Jr., author
Wadsworth, 2009
Buku Teks
Rourke, John T., author
Mc Graw Hill, 2009
Buku Teks
Hsuan-yi Chou, author
Artikel Jurnal
Princeton University Press, 1980
Buku Teks
Soltau, Roger H.
Longmans, Green , 1951
Buku Teks