Answer:
The answer is A. skeletal and muscular systems
Step-by-step explanation:
the skeletal muscle systems is responsible for the movements of many of the vertebrate living beings. The skeleton of the birds is highly adapted for the flight. It is extremely light in weight but strong enough to withstand the stress of takeoff, flight and landing. The largest muscles in the bird are the pectorals, which control the wing; these provide the powerful blow of wings, essential for the flight.