If a city is growing rapidly despite a low birth rate, which process may be dominant?

Correct answer: In-migration

Direct answer: Option B is correct. A city’s population changes through births, deaths and migration. If the birth rate is low, births alone are unlikely to explain rapid growth. A large inflow of people from villages, other towns or other regions can add many residents in a short time. This process is called in-migration. Option A, death rate, cannot itself add people; a high death rate would tend to reduce growth. Option C, soil formation, is a physical process and has no direct demographic meaning. Option D, natural decrease, occurs when deaths exceed births, so it would reduce the population rather than explain rapid growth. The question asks what can offset a low birth rate, so look for a process that adds residents from outside. A useful memory cue is: “in” means people come in, so in-migration can raise a city’s population even when natural increase is small.