Wehman, Paul
McGraw-Hill, 1981
Buku Teks
Jenkinson, Josephine C.
Routledge, 1997
Buku Teks
Yell, Mitchell L.
Prentice-Hall, 1998
Buku Teks
Lynch, James, author
World Bank, 1994
Buku Teks
Jeffree, Dorothy Moud, 1913-, author
Souvenir Press, 1994
Buku Teks