London; Cassell LTD., 1978
Buku Referensi
England Longman 1983
Buku Referensi
Barnhart, Clarence
Garden City, New York, Doubleday, 1967
Buku Referensi
Menge, Herman, author
Berlin Langenscheidt 1961
Buku Referensi
Krause, Wayne B
Jakarta: Elex Media Komputerindo, 2002
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