Ryan, William T.
Learning System Company, 1971
Buku Teks
Ryan, William T
Richard D. Irwin, 1980
Buku Teks
Ryan, William T.
Richard D. Irwin, 1981
Buku Teks
Ryan, William
Learning System of Company, 1971
Buku Teks
Berkowitz, Eric N.
St. Louis, Times Mirror/Mosby College Pub
Buku Teks