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Dyfyniad Arddull ChicagoGrigg, D B. Agricultural Systems of the World: An Evolutionary Approach. New York: Cambridge University Press, 1974.
Dyfyniad MLAGrigg, D B. Agricultural Systems of the World: An Evolutionary Approach. Cambridge University Press, 1974.
Rhybudd: Mae'n bosib nad yw'r dyfyniadau hyn bob amser yn 100% cywir.