求助！

xingxc11

Networks of blood vessels in bats’ wings serve only to disperse heat generated in flight. This heat is generated only because bats flap their wings. Thus paleontologists’ recent discovery that the winged dinosaur Sandactylus had similar networks of blood vessels in the skin of its wings provides evidence for the hypothesis that Sandactylus flew by flapping its wings, not just by gliding.

The argument in the passage relies on which of the following assumption?

(A)    Sandactylus would not have had networks of blood vessels in the skin of its wings if these networks were of no use to Sandactylus.
(B)    All creatures that fly by flapping their wings have networks of blood vessels in the skin of their wings.
(C)    Winged dinosaurs that flapped their wings in flight would have been able to fly more effectively than winged dinosaurs that could only glide.
(D)    If Sandactylus flew by flapping its wings, then paleontologists would certainly be able to find some evidence that it did so.
(E)    Heat generated by Sandactylus in flapping its wings in flight could not have been dispersed by anything other than the blood vessels in its wings.
选A 请各位给分析一下

sdcar2010

Necessary assumption. Use negation.

If you negate A), you have  Sandactylus would have had networks of blood vessels in the skin of its wings if these networks were of no use to Sandactylus.

If this is the case, the conclusion of the passage falls apart, since having the networks of blood vessels serves no purpose (no flapping) for Sandactylus. So A is the necessary assumption.