Beekman, George, author
Pretince Hall, 2002
Buku Teks
Attwood, Gaynor, author
McGraw-Hill, 1989
Buku Referensi
Meadows, A.J., author
Kogan Page, 1982
Buku Referensi
Longley, Dennis, author
Macmillan, 1982
Buku Referensi
Claus, Volker, author
Ellis Horwood, 1992
Buku Referensi