Nietzel, Michael T.
Prentice-Hall, 1998
Buku Teks
Nietzel, Michael T.
Prentice-Hall, 1987
Buku Teks
Trull, Timothy J., 1960-
Thomson , 2005
Buku Teks
Helen Beinart, Paul Kennedy, Susan Llewelyn, editor
BPS Blackwell, 2009
Buku Teks
Richards, Thomas William
McGraw-Hill, 1946
Buku Teks