Ross, Robert C.
McGraw-Hill, 1951
Buku Teks
Mellor, John W.
Cornell University Press, 1966
Buku Teks
Thomson, Edgar
Thomson Nelson and Sons Ltd. , 1949
Buku Teks
Elkan, Walter
The English Language Book Society ; Penguin Books, 1973
Buku Teks
the Australian Agricultural Economic Society, 1989
Majalah, Jurnal, Buletin