Roosevelt, Theodore, author
Prentice-Hall, 1961
Buku Teks
Kuebler, Roy R., author
John Wiley & Sons, 1976
Buku Teks
Smith, Elton Edward
Twayne Publishers, 1965
Buku Teks
Smith, William F., author
McGraw-Hill, 1993
Buku Teks
Smith, Wiliam F.
Harcourt Brace Jovanovich, Inc., 1983
Buku Teks