Final answer:
Sharon can see objects at night because she is relying on the cells in her eyes known as rods, which are sensitive to low light levels and enable vision in shades of gray.
Step-by-step explanation:
While walking at night, Sharon can easily see objects around her, thanks to the photoreceptors in her eyes called rods. These cells are highly sensitive to low light levels, enabling Sharon to see in the dark, although only in shades of gray. Rods are different from cones, which operate in bright light and are responsible for our ability to perceive colors. There are approximately 120 million rods in the human retina, allowing us to detect motion and navigate in low-light conditions. Unlike rods, cones are not sensitive enough to provide vision in very dark environments.