Pepall, Lynne, author
Thomson , 2005
Buku Teks
Waldman, Don E., author
Pearson, 2007
Buku Teks
Woodward, Joan, author
Oxford University Press, 1965
Buku Teks
Thompson, Arthur A., 1940-, author
Prentice-Hall, 1989
Buku Teks
Seckler-Hudson, Catheryn, author
Washington, D.C., The American University Press
Buku Teks