Palmer, Monte, author
Thomson Wadsworth, 2007
Buku Teks
MEI Publications Ltd, 2008
Majalah, Jurnal, Buletin
edited by Hilary Lewis Ruttley
[publisher not identified], 1995
Buku Teks
Bill, James A., author
Littel Brown and Company, 1984
Buku Teks
Goldschmidt, Arthur, author
Westview Press, 1983
Buku Teks