Why can migration have different local and national effects in population change?

Correct answer: Because people leaving one area can be added to another area

Direct answer: Option A. Migration involves movement of people between places, so its effect depends on the scale being studied. Suppose people move from a village to a city within the same country. The village loses population, while the city gains population. Thus, local populations change in opposite directions, but the national total does not necessarily change because the same people remain inside the country. If people cross an international border, one country may lose residents and another may gain them; again, migration redistributes people rather than creating them. Option B is wrong because migration does not always increase a country’s total population. Option C is wrong because migration directly changes local population. Option D is wrong because migration is movement, not birth rate. Memory cue: “local distribution changes; internal national total usually does not.”