McKenzie, Richard B., author
McGraw-Hill, 1980
Buku Teks
edited by Arthur L. Grey and John E. Elliot
Houghton Mifflin, 1965
Buku Teks
McConnell, Campbell R., author
McGraw-Hill, 1966
Buku Teks
Artikel Jurnal
Precious, Mark, author
Clarendon Press , 1987
Buku Teks