Question ID:PT86 S1 Q10 Passage:When a bird flies, powerful forces converge on its shoulder joints. The bird's wings must be kept stable during flight, which cannot happen unless something balances these forces. The only structure in birds capable of balancing them is a ligament that connects the wing to the shoulder joint. So that ligament must be _______. Stem:Which one of the following most logically completes the argument? Correct Answer Choice:EChoice A:the only structure that is indispensable to bird flight Choice B:the reason that a bird's wings must be kept stable during flight Choice C:the sole connection between the wing and the shoulder joint Choice D:the source of the powerful forces that converge on the shoulder joint Choice E:the means by which a bird stabilizes its wings during flight