Which growth strategy involves selling more of a firm's existing products to the firm's existing markets?

A) diversification
B) market penetration
C) market development
D) product development

Market penetration involves increasing sales of existing products to existing markets through strategies such as pricing promotions, advertising, and salesforce expansion. It does not involve developing new products or expanding into new markets, which are the focus of product development and market development, respectively. Diversification involves entering new markets with new products, which is more of a high-risk/high-reward strategy. Therefore, in this scenario, market penetration is the most appropriate growth strategy.