Keith, Arthur, Sir
Watts & Co., 1950
Buku Teks SO
Ruse, Michael
Cambridge University Press, 2012
Buku Teks SO
Richardson, W. Norman
Macmillan, 1976
Buku Teks SO
Eckhardt, Robert B.
McGraw-Hill, 1979
Buku Teks SO
edited by Lori D. Hager
Routledge, 1997
Buku Teks