MD : Bernan Press, 2004
Buku Teks
Holloway, William Vernon, author
McGraw-Hill , 1951
Buku Teks
The Office , 1981
Buku Teks
Wilson, Woodrow
Columbia University, [date of publication not identified]
Buku Teks
Brown, Everett S.
Appleton-Century-Crofts, Inc., 1950
Buku Teks