Basic Books, Inc., 1966
Buku Teks
Gray, Richard, 1944-, author
Longman, 1991
Buku Teks
Bogan, Louise, author
Henry Regnery, 1951
Buku Teks
Dembo, L.S., author
University of California Press, 1966
Buku Teks
Stepanchev, Stephen, author
Harper and Row, 1965
Buku Teks