A bird flies by moving its wings up and down. Which two systems are most directly responsible for the movement of a bird's wings?

A.

skeletal and muscular systems

B.

respiratory and muscular systems

C.

skeletal and digestive systems

D.

respiratory and digestive systems

A. Skeletal and muscular

the other three don't have to do with this type of internal movement though as the abdominal region and internal organs don't have to do with this, A is the only possible answer

The answer is A. skeletal and muscular systems

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.