Ranney, Austin
Holt, Rinehart and Winston , 1958
Buku Teks SO
Russell Sage Publication, 2001
Buku Teks SO
Saffell, David C.
McGraw-Hill, 1997
Buku Teks
Cook, Timothy E.
The University of Chicago Press, 1997
Buku Teks SO
Atkins, Ruth
John Wiley & Sons, 1980
Buku Teks