Martin, Anne
Routledger Kegan Paul, 1958
Buku Teks
Black, John Donald
Macmillan, 1953
Buku Teks
Wilcox, Walter W.
Prentice-Hall, 1951
Buku Teks
Cohen, R.L.
University Press, 1955
Buku Teks SO
Ewell, Peter T.
Ithaca, N.Y. Department of Agricultural Economics Cornell University 1984,
Buku Teks