I'm pretty sure it's immigration. The people performing that action is called immigrants. So, the act of moving to one nation from another is called immigration.
Benefits- The people have choice in who runs the country and which laws to place, and No rash decisions can be made without confirmation from multiple parties
Challenges- the first voting of the new leader, and setting up representatives for the new government
The answer would be B since when a city is undergoing urbanization people are moving in and not leaving.
