Passage Summary: Flying puts a lot of pressure on a bird's shoulders, and since a specific ligament is the only thing keeping the wings steady against those forces, that ligament is doing all the heavy lifting.

Conclusion: The specific ligament connecting the wing to the shoulder must be the component that withstands the intense physical stress of flight.

Reasoning: Flight creates powerful forces that must be balanced for stability, and this ligament is the only structure in the bird's body capable of balancing those forces.

Analysis: This is a 'Must be True' style completion where we are synthesizing facts. If the forces must be balanced for flight to occur, and the ligament is the only structure capable of doing so, it logically follows that the ligament is under significant tension or stress during flight. Look for an answer that confirms the ligament is the recipient of those powerful forces.