Denhardt, Robert B.
Wadsworth and Cengage Learning, 2014
Buku Teks
Denhardt, Robert B.
Harcourt College, 1999
Buku Teks
Herring, E. Pendleton
McGraw-Hill, 1936
Buku Teks
Simon, Herbert A.
Alfred A. Knopf, 1973
Buku Teks
Bartholomew, Paul C.
Littlefield, Adams, 1959
Buku Teks