Ian Beardwell, Len Holden
Prentice-Hall, 2001
Buku Teks
Agus Dharma, author
Rajawali Pers, 1991
Buku Teks
J. Winardi, author
RajaGrafindo Persada, 2002
Buku Teks
Jenks, James M.
New Jersey : Alexander Hamilton Institute, Inc,
Buku Referensi
Gazda, George M., author
Allyn and Bacon , 1975
Buku Teks