editor in chief, Charles A. Ford
Encyclopedia Britannica Educational Corporation, 1969
Buku Referensi
Winson, Nicola V., author
Elsevier, 2005
Buku Teks
Saunders, 2003
Buku Teks
Burden, Ernest E., 1934-, author
McGraw-Hill, 2012
Buku Teks
Maddex, Robert L., author
Routledge, 1996
Buku Referensi