Nelson, Carl A.
McGraw-Hill, 2000
Buku Teks
Caves, Richard E.
Harper Collins College Publishers, 1996
Buku Teks
edited by Bert N. Adams, Jan Trost
Sage Publications, 2005
Buku Referensi
Das, Bhagirath Lal
Zed Books, 1999
Buku Teks
Foster, Douglas
Macmillan, 1985
Buku Teks