Hames, Joanne Banker, author
Prentice-Hall, 1998
Buku Teks
Duett Edwin H
Harper & Row Publisher, 1990
Buku Teks
Cahill, Fred V.
The Ronald Press Company, 1952
Buku Teks
Nash, Bradley D.
Macmillan, 1959
Buku Teks
Powell, Fred Wilbur
Brookings Institution, 1939
Buku Teks