Final answer:
Harley-Davidson's extension into boots, helmets, and leather jackets represents a related diversification strategy, focusing on products that complement their motorcycles and target the same customer base.
Step-by-step explanation:
Harley-Davidson selling a line of boots, helmets, and leather jackets suggests that the firm is pursuing a strategy of related diversification. Related diversification is a strategy where a company expands its operations into areas that are similar to its current line of business. This is evident in Harley-Davidson’s case as boots, helmets, and leather jackets complement their primary product of motorcycles by enhancing the riding experience and are targeted towards the same customers.
The other options such as cost leadership, conglomerate diversification, geographic expansion, and horizontal integration do not align with the firm's extension of its product line into complementary accessories and apparel.