Final answer:
Product development strategies involve developing and selling new products to people who are already purchasing the firm's existing products.
Step-by-step explanation:
The strategy that involves developing and selling new products to people who are already purchasing the firm's existing products is called product development strategies. This strategy focuses on creating new products that appeal to the current customer base of the firm. By introducing new and innovative products, the firm can increase demand and encourage existing customers to make additional purchases.