Williams, Frederick
Harcourt Brace Jovanovich College Publishers, 1992
Buku Teks
Knoke, David, author
Thomson, 2002
Buku Teks
Hays, William Lee, 1926-1995, author
Holt, Rinehart and Winston, 1973
Buku Teks
Healey, Joseph F., 1945-, author
Cengage Learning, 2016
Buku Teks
Linneman, Thomas J., author
Routledge, 2018
Buku Teks