If a country's population growth rate becomes zero but positive net migration later increases, what effect can this have on total population?

Correct answer: Population may begin growing again

Total population changes through natural increase or decrease and net migration. If the overall growth rate is zero at first, additions and losses are balanced at that time. Later, positive net migration means more people enter the country than leave it. Unless an exactly offsetting change in births and deaths occurs, these additional residents raise the total population. Thus a zero growth rate at one moment does not permanently fix the population.

Option B is correct because positive net migration can restart population growth. Option A would require total losses to exceed additions, which is not stated. Option C is too strong: migration does not make the population double immediately; the amount depends on the number of migrants and the initial population. Option D is false because migration directly changes the population count. The result depends on net migration, not merely the number entering without considering those leaving.