Pfiffner, John M., author
Ronald Press, 1960
Buku Teks
Denhardt, Robert B., author
Harcourt College, 1999
Buku Teks
Henry, Nicholas
Prentice-Hall, 1975
Buku Teks
Denhardt, Robert B., author
Thomson, 2009
Buku Teks
Nigro, Felix A., author
Harper and Row , 1977
Buku Teks