The answer would be:
DNA : A A T T G C 
mRNA: U U A A C G 
The base pairings in mRNA is essentially the same, T to A, G to C however, uracil with substitute thymine to pair up with an Adenine base. In summary:
G to C C to G
A to U T to A
 
        
                    
             
        
        
        
I’ve annotated your question and colour coded the answer, (the dotted line represents current bird population) and blue line represents what the population will look love after natural selection
 
        
        
        
I'd say the answer is C but I'm not 100% sure. If not C then maybe B