Which characteristic is common to adult insects?

Adult insects are characterized by having six jointed legs, which is a defining trait of the class Insecta. This hexapod structure allows for a wide range of movement and adaptation to various environments. The six legs are typically arranged in three pairs, with each pair providing support and mobility as insects navigate through their habitats. This characteristic is essential for their survival, as it enables them to run, jump, climb, and fly, depending on the species.

The other choices do not accurately describe adult insects. For instance, eight jointed legs are typical of arachnids, not insects. Additionally, the structure of insects includes three main body regions—head, thorax, and abdomen—rather than four. Finally, insects do not have non-jointed legs; the jointed structure is crucial for their locomotion and overall functionality. Understanding these fundamental traits helps in the identification and classification of insects within the broader category of arthropods.