Final answer:
The stages of change model is best described as having a spiral shape, as it reflects the cyclical nature of how individuals progress and sometimes revisit stages before achieving lasting change.
Step-by-step explanation:
The stages of change model, which is often referred to as the Transtheoretical Model, does not adopt either a purely linear or purely spiral shape. Instead, the model is conceptualized more like a spiral. People often move through the different stages of change in a cyclical manner, meaning that a person may revisit certain stages multiple times before achieving lasting change. This cyclical nature means that the model takes on a spiral form rather than being a straightforward linear progression from start to finish. Therefore, the correct answer is b) Spiral.