Which of the following sets of characteristics is unique to Class Aves?

Step-by-step solution

According to NCERT, the characteristic features of Aves (birds) are the presence of feathers and forelimbs modified into wings. Their endoskeleton is fully ossified (bony) and the long bones are hollow with air cavities (pneumatic). Pinna is a unique mammalian character, not found in birds. Birds have a completely four-chambered heart, making the option with a three-chambered heart incorrect. Birds possess pneumatic bones, not solid bones, which helps in reducing their body weight for flight. Answer: Feathers, pneu