edited by Maxine Melling
Facet Publishing, 2005
Buku Teks
Armstrong, Michael, author
Crest Publishing House, 1999
Buku Teks
Smyth, Terry, author
Macmillan, 1996
Buku Teks
Davies, David B., author
McGraw-Hill, 1985
Buku Teks
Fisher, David T.
Prentice-Hall, 1991
Buku Referensi