Held, Colbert C., author
Westview Press, 1989
Buku Teks
Held, Colbert C.
Westview Press, 2014
Buku Teks
Palmer, Monte, author
Thomson Wadsworth, 2007
Buku Teks
Harari, Maurice, author
Prentice-Hall, 1962
Buku Teks
Bill, James A., author
Littel Brown and Company, 1984
Buku Teks