Korten, David C., author
Kumarian Press, 1990
Buku Teks
Palmer, Monte, author
Thomson Wadsworth, 2007
Buku Teks
Elin Diamond
Routledge, 1996
Buku Teks
Hammond, John Lawrence, 1872-1949, author
Penguin Books, [1947]
Buku Teks
Frederick A. Praeger, 1969
Buku Teks