Weis, Erich, author
National Textbook Company, 1993
Buku Referensi
Wichman, K., author
New York, David Mckay Company
Buku Referensi
Tiger Books International, 1994
Buku Referensi
London, London Longmans
Buku Referensi
Goulden, W. O., author
Little, Brown, 1955
Buku Referensi