Naisbitt, John, author
William Morrow, 1990
Buku Teks
Packer, Herbert L., author
McGraw-Hill, 1973
Buku Teks
Redstone, Louis G.
New York: McGraw-Hill, 1981
Buku Teks
edited by Julian Hilton
Macmillan, 1993
Buku Teks
edited by Davis S. Miall
Clarendon Press, 1990
Buku Teks