Bogardus, Emory S.
Macmillan, 1954
Buku Teks
Jonathan H. Turner
Springer, 2012
eBooks
Healey, Joseph F., 1945-, author
Pine Forge Press, 1998
Buku Teks
Schaefer, Richard T, author
New York, 2003
Buku Teks
Schaefer, Richard T, author
McGraw-Hill, 1995
Buku Teks