Janda, Kenneth
Cengage Learning, 2012
Buku Teks SO
McKenna, George
McGraw-Hill, 1998
Buku Teks SO
by John G. Geer [and others]
Wadsworth and Cengage Learning, 2012
Buku Teks SO
Geer, John Gray
Wadsworth and Cengage Learning, 2012
Buku Teks SO
Millspaugh, Arthur Chester, 1883-1955
The Brookings Institution, 1942
Buku Teks