Martin, Dick, author
American Management Association, 2007
eBooks
Albright, Madeleine, author
Harper Perenial, 2008
Buku Teks
Hitchcock, Terrance S.
Dow Jones-Irwin , 1982
Buku Teks
Kennedy, Robert F., 1925-1968, author
Harper & Row , 1962
Buku Teks
Winpisinger, William W., author
Colorado Westview Press, 1989
Buku Teks