Jenks, James M.
New Jersey : Alexander Hamilton Institute, Inc,
Buku Referensi
Chruden, Herbert J.
South-Western, 1966
Buku Teks
Goyal, R.C., author
Prenctice Hall of India, 1998
Buku Teks
McGraw-hill book , 1950
Buku Teks
Pigors, Paul, author
McGraw-Hill Book Company, Inc, 1956
Buku Teks