Tuggle, C.A, author
McGraw-Hill, 2013
Buku Teks
Izard, Halph S., author
Hunt Publishing Company, 1977
Buku Teks
Berner, R. Thomas, author
Allyn and Bacon, 1992
Buku Teks
Kansas City : University of Missouri
Majalah, Jurnal, Buletin
Craig, Richard, author
Thomson/Wadsworth, 2005
Buku Teks