Answer: (iii) Spiral model

The Spiral model (Boehm, 1986) is the SDLC model that explicitly emphasizes risk analysis at every phase of development. Each loop (iteration) of the spiral walks through four quadrants:

1. Determine objectives (of the current iteration),
2. Identify and resolve risks — risk analysis/prototyping of risky areas,
3. Development and testing of the product increment,
4. Planning of the next iteration (customer evaluation/review).

The radius of the spiral grows with each iteration, and each pass increases the level of the product. Because the model returns to risk analysis in every loop, it is the best fit for large, high-risk, and complex projects.

Why the others are wrong:

• (i) Waterfall — a purely linear, sequential model with no explicit risk-analysis step.
• (ii) Incremental — delivers the product in parts; risk analysis is not its defining feature.
• (iv) Prototype — focuses on building throwaway prototypes to clarify requirements, not on iterative risk analysis.