Ziegler, Kathleen
Rockport Publishers, 1994
Buku Referensi
Shannon, Faith
Reed International Books, 1987
Buku Referensi
Ferre, John P
Columbus : Charles E. Merril Publishing company,1983,
Buku Referensi
Atkinson, Jennifer L.
Rockport, 1996
Buku Teks
Luker, Leslie G.
Adana, 1973
Buku Teks