Cross, Wilbur
Prentice-Hall, 1995
Buku Referensi
Collin, P. H.
Peter Collin Publishing, 2001
Buku Teks
Greener, Michael
Penguin books, 1994
Buku Referensi
Statt, David A.
Routledge, 1999
Buku Referensi
Kurian, George Thomas
Amacom, 2013
Buku Referensi