Porter, Richard C.
Homewood, Ill. Richard D. Irwin 1982,
Buku Teks
Hildebrand, David K., 1940-, author
Duxbury Press, 1996
Buku Teks
Bartz, Albert E
Macmillan, 1981
Buku Teks
Reynolds, Lloyd G., author
Yale University Press, 1971
Buku Teks
Reynold, Lloyd George
McGraw-Hill, 1981
Buku Teks