Final answer:
Gradual transitions and harmonious elements are most likely to achieve calm stability in a design without being monotonous. Symmetrical balance provides formality and stability, while variety is necessary for interest, but should be used without creating imbalance.
Step-by-step explanation:
The option that is most likely to achieve calm stability in a design without being monotonous is gradual transitions and harmonious elements.
These techniques involve creating a subtle progression in elements such as color or shape and using elements that naturally complement each other.
For example, a pattern that integrates a smooth gradient from one color to another, or introduces repetitions of a curved shape, would create both unity and variety without overwhelming the design.
It is important to balance the elements to provide a visually pleasing experience without too much predictability or chaos.