Dyere, Everett D.
McGraw-Hill, 1979
Buku Teks SO
Cobb, Nancy J.
Mayfield , 2001
Buku Teks SO
Abramson, Paul R.
A Division of Congressional Quarterly, 1986
Buku Teks SO
Cobb, Nancy J.
Mayfield Publishing, 2000
Buku Teks SO
Macmillan, 1990
Buku Teks SO