In response to the need to develop greater and greater mass markets for their products, American business in the 1920s relied especially on the new techniques of

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Quizplus · Accepted Answer

The question asks specifically for the technique(s) used to develop greater mass markets, and the most effective one during the 1920s was consumer advertising. This allowed businesses to reach a wider audience and promote their products to potential customers, ultimately increasing demand and sales. While other techniques such as product variation, price competition, and direct selling were also used, they were not as effective in generating mass markets as consumer advertising. Therefore, D is the best choice.

In Response to the Need to Develop Greater and Greater