Why is the respiratory system of a bird more efficient than the human respiratory system? A) The bird respiratory system does not mix exhaled air with inhaled air.
B) A bird lung contains multiple alveoli, which increases the amount of surface area available for gas exchange.
C) The human respiratory system ends in small parabronchi, which reduce the amount of surface area available for gas exchange.
D) Only B and C are correct. E) A, B, and C are correct.

Option A.

The bird respiratory system does not mix exhaled air with inhaled air.

Explanation:

The respiratory system of birds are more efficient than that if humans because The bird respiratory system does not mix exhaled air with inhaled air and this is due to the fact that their lungs are u directionally ventilated instead of bidirectional flow of other organisms. The lungs undirectional is as a result of inflation and deflation of air sacs in a sequence which make the exhaled air not to mix with inhaled air.

any abiotic or biotic factor in an ecosystem that causes a population's size to slow or decrease is a limiting factor.