Dubois, Brenda, 1949-
Allyn and Boston, 1992
Buku Teks
Gore, M.S.
Asia Publishing House, 1965
Buku Teks
Cohen, Nathan Edward
National Ass. of Workker, 1964
Buku Teks
Gray, Ivan
Learning matters Ltd., 2010
Buku Teks
Hepner, Harry W.
Prentice-Hall, 1971
Buku Teks