Wyatt, Wendy, author
Glorier International, 1999
Buku Referensi
Greene, Gardiner G., author
McGraw-Hill, 1975
Buku Teks
Humphries, john, author
Glorier International, 1999
Buku Referensi
Hunt, Nigel, author
Glorier International, 1997
Buku Referensi
Artikel Jurnal