I had the same question and the answer was C OR A.
In this question, there are no options given to choose from. So i would answer this question based on my knowledge. The most likely cause of the observed variation is adaptation and evolution. The birds of that island adapted to the food source and then they evolved as per the requirement of the place and food source.
<em>Genetic codes contains <u>ORGANISMS.</u></em>
The two DNA<span> strands are known as polynucleotides since they are </span>composed<span> of simpler units called nucleotides. Each nucleotide is </span>composed<span> of a nitrogen-containing nucleobase—either cytosine (C), guanine (G), adenine (A), or thymine (T)—as well as a sugar called deoxyribose and a phosphate group.</span>
Replication Fork! Is the answer! Hope this helps!