Cassar, Mario-Paul, author
Quantum Publishing, 2000
Buku Referensi
Tappan, Frances M.
Appletton & Lange , 1998
Buku Teks
Maxwell-Hudson, Clare, author
Dorling Kindersley, 1988
Buku Referensi
Young, Jacqueline
London Thorsons 1992,
Buku Teks
Rush, Anne Kent
Aqurian , 1994
Buku Teks