Answer:
Option (A).
Step-by-step explanation:
Evolution may be defined as the change in the characteristics of a species over several generation with time. Natural selection acts as a main drivinf force for the evolution.
The drought of 1977 is responsible for the species evolution. The species is larger in this case (as mentioned in the question) and the species has deeper beaks over time. The birds have relatively large and deep beaks because they can easily crack the food.
Thus, the correct answer is option (A).