Final answer:
Curved lines have a softening effect on the composition.
Step-by-step explanation:
The type of line that has a softening effect on the composition is curved lines. Curved lines are expressive and organic, adding a dynamic and flowing character to a work of art. They are often found in nature and can create a more varied and visually appealing composition. For example, in the painting Laocoon Group, the figures' flailing limbs and the sinuous form of the snakes are made up of expressive, curved lines.