Dorrance & company, 1972
Buku Teks
Fusfeld, Daniel Roland, 1922-, editor
Scott, Foresman and Company, 1986
Buku Teks
Maurice, S. Charles
McGraw-Hill, 2002
Buku Teks
Fuchs, Victor R.
Basic Books, 1974
Buku Teks
Commons, John R.
Macmillan, 1956
Buku Teks