Smart, Terry L., author
Holt, Reinhart and Winston, 1987
Buku Teks
London Chancellor Press 1999,
Buku Referensi
Dorling Kindersley, 1998
Multimedia
Honour, Hugh, author
Laurence King Publishing, 1995
Buku Referensi
Fuller, John Frederick Charles, author
Funk and Wagnalls, 1955
Buku Teks