Dyke, Vernon van
Nelson, 1992
Buku Teks
Merriam, Charles E. (Charles Edward)
University of Chicago Press, 1957
Buku Teks
Tansey, Stephen D.
Routledge, 1996
Buku Teks
Pye, Keith
Stanley Thornes , 1992
Buku Teks
Carter, Gwendolen M.
Praeger, 1973
Buku Teks