Answer:
The correct answer is option A.
Step-by-step explanation:
According to the given question environmental changes made it difficult for the birds with short and wide beaks to find food due to which their gene pool disappeared after few generations.
Environmental changes favoured the birds with long and narrow beaks due to which this trait was passed on to their generations and after few generation-long and narrow beak birds will dominate the niche. This is an example of genetic drift where the population has shown the directional shift.
Thus, option A is the correct option.