GMAT Reading Comprehension (RC) | Re: The fossil remains of the first flying vertebrates, the pterosaurs

Hello

Please clarify my doubt regarding question 3, My answer is C. Please tell how B can distinguish pterosaur from a bird?
C) anatomic origin of its wing strut - clearly distinguish it from bird
B) both of them have hollow bones - A common feature and it wont distinguish right?

Thanks!

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