Which one of the following does the author offer as an argument against gray marketing? A. Manufacturers find it difficult to monitor the effectiveness of promotional efforts made on behalf of products that are gray marketed. B. Gray marketing can discourage product promotion by authorized distributors. C. Gray marketing forces manufacturers to accept the low profit margins that result from quantity discounting. D. Gray marketing discourages competition among unauthorized dealers. E. Quality standards in the manufacture of products likely to be gray marketed may decline.