Somers, Herman Milles, author
Brookings Institution, 1962
Buku Teks
Hogue, Kathleen
Welker, 1988
Buku Teks
Baker, Judith J., author
Jones and Bartlett Publishers, 2011
Buku Teks
Cleverley, William O., author
Aspen Publication, 1997
Buku Teks
Cleverley, William O., author
Jones Bartlett Learning, 2011
Buku Teks