Final answer:
Birds are endothermic and can maintain a constant body temperature, essential for flight and metabolic activity. Feathers provide insulation while special lung adaptations aid in temperature regulation. The final answer is C. endotherms.
Step-by-step explanation:
All birds are classified as being endothermic, which means they are capable of maintaining a constant internal body temperature despite changes in the environment. This characteristic is essential for sustaining their high metabolic rates, especially necessary for the energy demands of flight. Birds belong to the class Aves and share key features such as being warm-blooded, having two legs, and laying eggs.
Endothermy in birds is facilitated by adaptations such as feathers for insulation and a one-way airflow system through their lungs, which helps in temperature regulation. Birds evolved from dinosaurs and are considered endothermic amniotes. Unlike ectotherms, which rely on environmental heat to regulate their body temperature, birds generate internal heat to keep cellular processes operating efficiently in cooler environments.
"All birds are __________." is: C. endotherms.