Option (B) accommodation is correct. According to the textbook, 'The ability of the eye to focus on both near and distant objects, by adjusting its focal length, is called the accommodation of the eye.' The ciliary muscles modify the curvature of the eye lens, which changes its focal length—when muscles relax, the lens becomes thin and focal length increases for seeing distant objects; when muscles contract, the lens becomes thicker and focal length decreases for seeing nearby objects. Options (A), (C), and (D) are incorrect because presbyopia, near-sightedness (myopia), and far-sightedness (hypermetropia) are all refractive defects of vision, not the normal ability of the eye to adjust focus.