Ferre, John P
Columbus : Charles E. Merril Publishing company,1983,
Buku Referensi
Day, Robert A., author
ISI Press, 1983
Buku Teks
Ziegler, Kathleen, author
Rockport Publishers, 1994
Buku Referensi
Artikel Jurnal
editor, James P. Casey
John Wiley & Sons, 1980
Buku Teks