Which of the following life-cycle models is based on continuous flow of work?

The Lean life-cycle model is based on a continuous flow of work. In Disciplined Agile, Lean focuses on minimizing waste, delivering value continuously, and optimizing the entire value stream. Unlike other models like Waterfall, which follow a sequential approach, or Agile models, which may focus on iterative increments, Lean emphasizes a smooth, steady flow of value to the customer. Continuous Delivery Agile also involves a continuous flow, but "Lean" specifically is the framework built around this concept. Therefore, "D. Lean" is the correct answer.