Williams, Peter J
Longman, 1982
Buku Teks
Williams, David J., author
Prentice - Hall , 1971
Buku Teks
McConnell, David, author
McGraw-Hill, 2010
Buku Teks
Day, Robert W., author
McGraw-Hill, 1999
Buku Teks
Ramsey, William L., author
Holt, Rinehart and Winston, 1961
Buku Teks