Skees, William D.
Lifetime learning , 1981
Buku Teks
Wolberg, John R.
Prentice-Hall, 1983
Buku Teks
Gorsline, G. W.
Prentice-Hall, 1980
Buku Teks
Abrams, Marshall D.
Addison-Wesley, 1973
Buku Teks
Holzberlein, Deanne
The Haworth Press, Inc., 1986
Buku Teks