Benham, Frederic
New York, N.Y. Pitman 1947,
Buku Teks
Benham, Frederic
New York, N.Y. Sir Issac Pitman 1941,
Buku Teks
Lutz, Vera
Oxford University Press , 1962
Buku Teks
Case, Karl E., author
Pearson, Prentice Hall, 2009
Buku Teks
Mankiw, N. Gregory, author
Harcout College, 1998
Buku Teks