Final answer:
Animals are classified by traits including group behavior, symmetry, and developmental characteristics. Group behavior is a key trait that distinguishes different animal species. The correct answer is option D.
Step-by-step explanation:
Animals can be identified by specific traits which are used to classify them within the animal kingdom. One of the characteristics used to identify animals is group behavior, which involves interactions with other members of the same species, such as social activities and cooperative living. Other important characteristics for classification include symmetry, the number of germ tissue layers formed during development, and the presence or absence of an internal body cavity.