Seckler-Hudson, Catheryn, author
Washington, D.C., The American University Press
Buku Teks
Brown, Alvin
Prentice-Hall, 1947
Buku Teks
written by M. C. Barnes [and others]
Allen & Unwin, 1970
Buku Teks
Brown, Alvin
Hibbert Printing Company, 1945
Buku Teks
Dale, Ernest, author
New York, N.Y., American Management Association
Buku Teks