Final answer:
The statement regarding the fusion of avian skeleton bones to create rigid structures for flight is true(A). Birds have a lightweight skeleton with fused bones and features like hollow bones connected to air sacs, optimizing flight.
Step-by-step explanation:
The statement Many bones of the avian skeleton are fused to form rigid structures is True(a). Birds have evolved to have a lightweight skeleton that is conducive to flight. To achieve this, many of their bones are indeed fused, which not only lightens the skeleton but also provides the necessary support and rigidity that birds need to fly effectively. Fused bones reduce the overall number of bones and the weight they would carry during flight. Examples of such fused structures include parts of the vertebral skeleton and the braincase. Furthermore, birds have adaptations like hollow or pneumatic bones with air spaces that can connect to air sacs and features such as a bony ridge along the breastbone to which the flight muscles attach. By reducing their body mass and consolidating bone structures through fusion, birds can more efficiently power and control their flight.