Eaglestone, Robert
Routledge , 2005
Buku Teks SO
Roberts, Edgar V.
Prentice-Hall, 1977
Koleksi Publik
Headrick, Paul, 1957-
Wiley-Blackwell, 2014
Buku Teks SO
Cambridge University Press, 1997
eBooks
Lerner, Laurence D.
Oxford University Press, 1954
Buku Teks SO