Reynolds, P.A., author
Longman, 1994
Buku Teks
Couloumbis, Theodore A., author
Prentice-Hall, 1990
Buku Teks
Pearson, Frederic S., author
McGraw-Hill, 1992
Buku Teks
edited by John Baylis and Steve Smith
Oxford University Press, 2006
Buku Teks
Griffith, Martin, author
Routledge, 2002
Buku Teks