In which situation can a city's population increase even when natural increase is low?

Correct answer: More people come from outside

Answer: A, more people come from outside. Natural increase is the balance between births and deaths. If that balance is small, a city can still gain population when many people move into it from other places. This movement into a city is called in-migration. The total population may therefore rise even though births minus deaths is low. Option A is correct because incoming residents add directly to the city’s population. Option B is incorrect because if everyone leaves, the population would fall. Option C is incorrect because zero births and zero in-migration provide no addition from either source. Option D is incorrect because a very high death rate tends to reduce natural increase, not increase the population. The exact result also depends on deaths and out-migration. Memory cue: natural increase is births minus deaths; total change also includes migration.