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