Concept:Air sacs are specialised respiratory structures found only in birds.Explanation:Poultry are birds, and their respiratory system includes air sacs.These air sacs connect to the lungs and allow a continuous, one-way flow of air.This makes breathing in birds more efficient than the two-way (in-and-out) breathing in mammals.Mammals such as rabbits, goats, and cattle do not possess air sacs.Answer:C. poultry