Final answer:
The Sustainability Model is the project selection model that emphasizes long-term success by focusing on sustainable development practices.
Step-by-step explanation:
The project selection model that focuses strongly on the long-term success of the firm is the Sustainability Model. This model emphasizes enduring growth and development by considering environmental, social, and economic impacts. It ensures projects align with sustainable practices, thus safeguarding the company's future. Other models, such as the US military model, Product Line Extension, and Competitive Necessity, may focus on specific aspects like strategy, expansion, or market competition, but not primarily on long-term sustainability.
Final answer in 2 lines: The Sustainability Model is the one that focuses on the long-term success of the firm. It balances various aspects to ensure sustainable development in the long run.