Healey, Joseph F., 1945-, author
Wadsworth, 1996
Buku Teks
Williams, Frederick
Harcourt Brace Jovanovich College Publishers, 1992
Buku Teks
Hinkle, Dennis E., author
Houghton Mifflin, 2003
Buku Teks
Knoke, David, author
Thomson, 2002
Buku Teks
Hays, William Lee, 1926-1995, author
Holt, Rinehart and Winston, 1973
Buku Teks