Siever, Ellen
O'Reilly, 2003
Buku Teks SO
Schaber, Gordon D.
West Publishing, 1990
Buku Teks
Folsom, Ralph Haughwout
West Group, 1999
Buku Teks
Maraist, Frank L.
West Publishing, 1996
Buku Teks
Arntz, Helmut
The Press and Information Office of the federal Germa Govermant, [1967]
Buku Teks SO