Final answer:
Southwest, Horizon, Frontier, and JetBlue are using a cost leadership strategy in the airline industry.
Step-by-step explanation:
Porter's Three Generic Strategies are a framework used to analyze competitive advantage in a business. The three strategies are cost leadership, differentiation, and focus. A cost leadership strategy involves offering products or services at lower prices than competitors while still maintaining acceptable quality.
Out of the given options, the companies using a cost leadership strategy are Southwest, Horizon, Frontier, and JetBlue (Option A). These airlines aim to provide low-cost flights to customers by focusing on efficiency and cost-saving measures.