Which of the following are characteristics of all insects?

The correct choice identifies two fundamental characteristics that define all insects: they possess six legs and are structured with three main body segments — the head, thorax, and abdomen. This classification is crucial for understanding the biology of insects, which belong to the class Insecta. The six legs allow insects to move efficiently and adapt to various environments, while the three segments facilitate different functions, such as sensory processing in the head, locomotion in the thorax, and digestion in the abdomen.

Other characteristics mentioned in the other choices might describe certain insects but do not apply universally to all. For instance, not all insects have wings; some, like ants and certain beetles in their larval stages, may not develop them at all. Similarly, while antennae are typical for insects, there are exceptions in various life stages. An exoskeleton is indeed a characteristic of insects, but not all insects possess gills, as many are adapted to terrestrial environments where gills would not be functional. Colorful patterns and large sizes may apply to specific species but do not define the insect class as a whole. Therefore, the attribute of having six legs and three body segments precisely delineates the insect category in a biological context.