What are the characteristics of birds and mammals?

I- Birds have a body adapted to flight, with hollow bones and air sacs that facilitate aerial flotation.
II- Birds have a circulatory system with double circulation, and their blood rich in oxygen does not mix with the poor one.
III- Birds have a digestive system adapted to their feeding habits, with a crop, stomach, and gizzard.
IV- Mammals have a body divided into head and trunk, four limbs, and in many of them, the vertebral column extends into a tail.
V- Mammals have a nervous system with a large brain, very effective in the development of instinct, learning, and behavior.
VI- Mammals have a modified mouth with fleshy lips, indispensable for the young to suckle.
a) I, II, III, IV, V, and VI are correct.
b) I, II, and III are correct.
c) IV, V, and VI are correct.