A key identifying characteristic of adult insects is:

A key identifying characteristic of adult insects is:

• A. Chewing mouthparts
• B. Two pairs of antennae
• C. Three pairs of jointed legs
• D. Four pairs of wings

Answer: (C)

Insects, as adults, all have six legs—three pairs attached to the thorax. That six-legged body plan is a consistent, universal feature across all adult insects, making it the most reliable identifying characteristic among the options. Other traits vary a lot: mouthparts differ (some insects chew, others sip or pierce), insects have a single pair of antennae (not two pairs), and wings are not universal (some adults are wingless or have different numbers of wings). Because the three pairs of jointed legs stay the same across all adult insects, this trait best distinguishes them.

Insects, as adults, all have six legs—three pairs attached to the thorax. That six-legged body plan is a consistent, universal feature across all adult insects, making it the most reliable identifying characteristic among the options. Other traits vary a lot: mouthparts differ (some insects chew, others sip or pierce), insects have a single pair of antennae (not two pairs), and wings are not universal (some adults are wingless or have different numbers of wings). Because the three pairs of jointed legs stay the same across all adult insects, this trait best distinguishes them.