Final answer:
Option (3), Earthworms use their skin to sense movement and light, as they lack complex visual organs. Their simple brain enables them to respond to environmental stimuli, and their skin is also vital for respiration.
Step-by-step explanation:
Earthworms utilize their skin to sense movement and light. Unlike some other worms, earthworms do not have eyes or eyespots to detect light; rather, their entire skin is sensitive to changes in light intensity. Earthworms have a simple brain that allows them to respond to environmental stimuli like light and touch, but they lack complex visual organs.
Their nervous system is relatively simple compared to other animals, but it is well adapted for their underground lifestyle, allowing them to sense vibrations and changes in the light levels that penetrate the soil. This sensitivity helps them navigate and avoid predators. Additionally, the earthworm's skin is crucial for respiration, as they breathe through their skin, which requires it to remain moist for gas exchange.