Kalvelage, Carl, author
Foresman, 1976
Buku Teks
Baglione, Lisa A., author
Thomson Wadsworth, 2007
Buku Teks
SAGE Reference, 2011
Buku Referensi
Johnson, Janet Buttolph, 1950-, author
CQ Press, 2012
Buku Teks
Garson, G. David., author
Holbrook Press, 1971
Buku Referensi