Dean, Howard H.
Prentice-Hall, 1962
Buku Teks
Bramer, George R., author
Charles E. Merrill Publishing Company, 1981
Buku Teks
Harris, Muriel, author
Prentice-Hall, 1997
Buku Referensi
Hewings, Martin, author
Cambridge University Press, 2006
Buku Teks
Muhibbin Syah, author
RajaGrafindo Persada, 2010
Buku Teks SO