Brewer, Richard, author
Saunders College Publishing, 1982
Buku Referensi
Brewer, Richard, author
Saunders College Publishing, 1982
Buku Teks
Smeins, Fred E., author
Drive Kendall/Hunt, 1978
Buku Teks
Cox, George W., author
Wm. C. Brown, 1996
Buku Teks
Brower, James E., author
Dubuque Wm. C. Brown , 1990
Buku Teks