Americana Corporation, 1980
Buku Referensi
Hiebert, Murray, author
Mc Graw-Hill , 2001
Buku Teks
Feather, Leonard, author
Horizon Press, 1960
Buku Referensi
edited by Kirsten Malmkjær, James M. Anderson
Routledge, 1991
Buku Referensi
Columbia University Press, 1950
Buku Referensi