Final answer:
Horns are permanent and made of bone and keratin, whereas antlers are shed annually and are entirely bone. Antlers are typically grown only by males, often to attract mates or assert dominance. Option A is correct.
Step-by-step explanation:
Horns are permanent structures that an animal retains throughout its life, while antlers are shed and regrown each year. Horns consist of a bony core covered by a protective keratin sheath, whereas antlers are entirely made of bone. Antlers typically exhibit a seasonal growth cycle, often linked to the mating season, in contrast to horns which grow continuously.
Additionally, in species with these features, sexual dimorphism is common. An example is the male moose, which grows antlers partly as a display to attract females and to compete with other males.