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 assumptions?

• ASandactylus would not have had networks of blood vessels in the skin of its wings if these networks were of no use to Sandactylus.  
• BAll creatures that fly by flapping their wings have networks of blood vessels in the skin of their wings.  
• CWinged dinosaurs that flapped their wings in flight would have been able to fly more effectively than winged dinosaurs that could only glide.  
• DIf Sandactylus flew by flapping its wings, then paleontologists would certainly be able to find some evidence that it did so.  
• EHeat generated by Sandactylus in flapping its wings in flight could not have been dispersed by anything other than the blood vessels in its wings.