Final answer:
Eusociality is found primarily in insects, especially ants, bees, and termites, which exhibit complex behaviors such as division of labor and cooperative brood care. The correct option is d).
Step-by-step explanation:
Examples of eusociality may be found among certain animal groups, notably within the insect group. Eusociality is characterized by complex social behaviors including cooperative brood care, overlapping generations within a colony of adults, and a division of labor into reproductive and non-reproductive groups.
Among insects, species like ants, bees, and termites exhibit eusocial behaviors. In contrast, while other groups such as mammals, birds, and primates may have complex social structures, they do not typically exhibit the stringent criteria defining eusociality as seen in insects. Therefore, the correct answer would be d) Insects.