Which form of the interrogative pronoun correctly completes the sentence? margaret wants to know bike this is. a. whose b. who's

The answer would be A. whose
B. who's would not make sense in this situation because who's is a contraction which means 'who is'. If that was to be used in the answer, the sentence would be, "Margaret wants to knwo who is bike this is," which makes no sense whatsoever

Whose shows possession 
Hope my answer helped! :)