Final answer:
Corrective lenses for nearsightedness and farsightedness work by compensating for lens abnormalities in the eye, using diverging and converging lenses, respectively, to properly focus light onto the retina.
Step-by-step explanation:
Graham is nearsighted and Grace is farsighted. Corrective lenses work for both of them because their respective visual disorders are caused by d) Lens abnormalities. Specifically, nearsightedness, or myopia, is an issue where the eye overconverges the light rays, causing images to focus in front of the retina, making distant objects appear blurry. To correct this, a diverging lens is used to spread out the light rays, moving the focal point back onto the retina.
On the other hand, farsightedness, or hyperopia, is when the eye underconverges light rays such that near objects are focused behind the retina, appearing blurry. A converging lens is used to correct this by focusing the light rays onto the retina. Both of these corrective lenses deal with the eye's inability to focus light properly due to the shape and flexibility of the lens within the eye.