Gray, Richard, 1944-, author
Longman, 1991
Buku Teks
Forrest-Thomson, Veronica, author
Manchester University Press, 1978
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