Dyke, Vernon van, author
Nelson, 1992
Buku Teks
Merriam, Charles E. (Charles Edward), author
University of Chicago Press, 1957
Buku Teks
Aldine Publishing Company, 1968
Buku Teks
Pye, Keith
Stanley Thornes , 1992
Buku Teks
Carter, Gwendolen M., author
Praeger, 1973
Buku Teks