Answer:
The correct answer is - A. immigration, emigration.
Explanation:
In biology, immigration is the act of joining or entering a new species or population of organisms into a particular area or population. These new species carry new alleles and traits with themself in the area and population increasing the population.
On other hand, emigration is the act of leaving the area where a population used to live due to changes in the habitat or the particular habitat is not suitable anymore for the population.