Colston, Catherine, author
Cavendish Publishing, 1999
Buku Teks
Panesar, Sukhninder, author
Longman, 2001
Buku Teks
Andrew Christie, Stephen Gare
Blackstone Press, 2001
Buku Teks
Haar, Charles M., author
Little, Brown, 1977
Buku Teks
Cunningham, Roger A., author
West Pub., 1993
Buku Teks