When can international migration change the total national population?

Correct answer: When people cross national borders to enter or leave

The direct answer is A. International migration involves people crossing the boundary of one country to enter another country or leave it. If people enter a country, they add to that country’s population; this is in-migration or immigration. If residents leave for another country, they reduce the population; this is out-migration or emigration. Therefore, international migration can change the national total. Option A states the essential condition: crossing a national border. Option B describes movement within one city, which is internal movement and does not change the country’s total. Option C says no border is crossed and therefore does not describe international migration; equal births and deaths would only make natural change zero. Option D concerns an institutional change, not population movement. Memory cue: a national total changes through births, deaths, or movement across the country’s border.