Answer:
The correct answer is option D. "moving from one country to another".
Step-by-step explanation:
There are different types of migration depending on the geographical place where people move and for how long. External migration is defined as people moving from one country to another either permanently or for a long period of time. External migration is comprised of two concepts: emigration, which is the exit of people from their country and; immigration, which is the enter of people into another country.