Holt, Renehart and Winston , 1971
Buku Teks
Parkin, Michael, 1939-
Prentice-Hall, c1992
Buku Referensi
Morley, Samuel A.
The Dryden Press, 1984
Buku Teks
Samuelson, Paul Anthony, 1915-2009
New York, 2005
Buku Teks
Lindauer, John
John Wiley & Sons, 1971
Buku Teks SO