edited by Sally C. Reynolds, Andrew Gallaghe
Cambridge University Press, 2012
Buku Teks
Elleh, Nnamdi, author
McGraw-Hill, 1997
Buku Teks
Estell, Kenneth
Visible Ink Press, 1994
Buku Teks
by Colin M. Turnbull
Simon and schuster, 1962
Buku Teks
Davidson, Basil, author
Time-Life International, 1967
Buku Teks