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Dyfyniad Arddull ChicagoZeithaml, Valarie A. Services Marketing. New York: McGraw-Hill, 1996.
Dyfyniad MLAZeithaml, Valarie A. Services Marketing. McGraw-Hill, 1996.
Rhybudd: Mae'n bosib nad yw'r dyfyniadau hyn bob amser yn 100% cywir.