Jacobs, Michael
Open University Press, 2006
Buku Teks SO
Kaplan, Harold I.
Williams & Wilklins , 1993
Buku Teks SO
Levine, Baruch
Prentince Hall, 1979
Buku Teks SO
Ettin, Mark F.
Allyn and Bacon, 1992
Buku Teks SO
Berne, Eric
Oxford University Press, 1969
Buku Teks SO