Griffith, Martin
Routledge, 2002
Buku Teks
edited by Beth A. Simmons and Richard H. Steinberg
Cambridge University Press, 2006
Buku Teks
Goodpaster, Gary
University of California, 1993
Buku Teks
Spero, Joan Edelman
Wadsworth, 2010
Buku Teks
Maps Com, 2007
Buku Referensi