When choosing between products to stock on its shelves, a retailer will always prefer a product with the highest contribution margin, irrespective of the time it takes to sell. always prefer a product with the highest contribution margin per unit floor space irrespective of how long it takes to sell. maximize its total contribution margin over a period of time, irrespective of floor space devoted to the product. always prefer a product with higher contribution margin per unit floor space over a period of time, such as a day or a week