Step 1: Understanding the Concept:
Rhythm in visual design principles is achieved through repetition, alternation, progression/gradation, radiation, and continuous line movement.
Step 2: Detailed Explanation:
In the principles of design:
Radiation is a method of creating visual rhythm where design lines, shapes, or motifs emanate and sweep outwards in all directions from a central focal point or axis (such as rays radiating from the sun, petals from a flower center, or spokes of a wheel).
Step 3: Final Answer:
Hence, when lines extend outwards from a central point, it is called Radiation, corresponding to option (D).