Nucleic acids. They contain a phosphate base and a nitrogen group. 
        
             
        
        
        
The forelimbs of all mammals are homologous traits, meaning that they originate from a common ancestral trait.
The correct answer is therefore C. Homologies (homologous traits), from the same common ancestor. 
(To clarify, we know it is from a common ancestor because both bats and humans are mammals)
 
        
             
        
        
        
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