Sally Burt, Daniel Añorve Añorve
Palgrave Macmillan, 2016
Buku Teks SO
Joy Hakim
Oxford University Press, 2003
Buku Teks
Boller, Paul F.
Houghton Mifflin , 1988
Buku Teks SO
Killblane, Richard E.
Emerald Publishing Limited, 2019
eBooks
Strober, Gerald S.
Harper Perennial, 1994
Buku Teks SO